Let me do an update, with pictures this time.
I ended up basically redoing everything. In large part because I should have stopped working hours before I did (note to self, you're better, but you're not all better. When confused, just stop and come back later).
My big screw up was the drilling of the set screw holes. What I should have done was more closely examined the drill guide and fixed the flashing that screwed up the way it mounted before I drilled. And I should not have simply gone nuts wallering out the hole. Ah well. Nothing I can do now, unless I chose to buy a new gear shaft. Which I don't think I need.
So here's a shot of the reverse gears mounted on the ends of the transmission gear shafts.
As you can see, the gear on the right is not exactly deeply mounted. There's just not that much to attach to. It's not shallow threaded by any means, but it's not deeply seated either. It's simply adequate, and a little visually disturbing.
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The left hand gear is the more worrysome because of the installation. That's the one I screwed up. but, as long as I behave using reverse, it really should all be just fine.
Here's the reverse unit slipped up onto the transmission.
This is it with the lever forward, in neutral for the reverse, letting the bike ride forward in a normal manner.
And here it is, with the lever back, in reverse. The main transmission must be in neutral.
I was surprised by the unevenness of the gear teeth engagement here. The right hand gear is much less deeply engaged. But, it's probably a non-issue as far as strength goes because again, I'm going to be gentle in reverse.
I was surprised when I buttoned it all up and was playing with it spinning the rear tire by hand that it was easy to get it only partially into reverse, with the gear teeth clicking instead of actually engaging. You have to very deliberately hold the lever down and pull back in order to fully and securely engage reverse. Which, after consideration, is probably not a bad thing. For you do not want to engage reverse accidentally or such. The picture above may well be the reverse not fully engaged and in clicking mode.
Minor disappointment here with regards to the longer mounting bolts. They did not come with the washer the oem ones had, and you cannot find the proper size washer at your hardware store and Harley does not sell them seperately. So you end up just grinding the head of the allen screw into the chrome case cover a bit. Not a big deal per-se, just a Grr disappointment.
And here's a few shots of the whole thing, all mounted up.
It's not big, it doesn't feel like it will get in the way at all. But boy does that ~1/2" create headaches with accessories and the exhaust.
And here's my hacked up chrome cover insert. Hacked up previously, when I should have stopped. It could be neater.
Lastly, the exhaust. I am not done with this part yet, and it took some time and was surprising. The exhaust runs down this side, with the front pipe clamped to a bracket that lived under the transmission cover. The rear pipe comes down just outside the rear edge of the transmission cover and joins in.
Because the reverse gear unit spaces out the mounting bracket, you end up pushing the exhaust over about half an inch. I did not like this at first. In fact I still don't. I was worried that this would put undue strain on the rather delicate exhaust mounting studs in the head. As well screw up pipe sealing.
I tried mounting up the exhaust just to the head studs, letting the retainers at the head hold the exhaust in place. To my surprise, done this way holds the exhaust outwards from the stock mounting location about 3/4", and it's still nearly 1/4" outward of the extended position of the mounting bracket with the reverse gear installed! So the oem mounting actually pulls the exhaust inboard quite hard.
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I'd thought I might be able to trim the exhaust bracket and get the exhaust back under the transmission cover. That cannot be done. Well, not without a whole lot of major pipe smashing, which I wasn't willing to do. The front pipe would have to be smashed down along the entire length of the transmission cover, and the rear pipe would have to be substantially dented to fit the rear edge of the transmission cover. The absolute killer is the smashing of the front pipe to go under the transmission cover includes the slip joint where the pipes join up. That's simply a no-go, so I'll leave the pipe shoved over outboard of stock about 1/2". This also explains why the kit didn't attempt to fix it. It could be done with custom pipes, but that would be quite expensive.
So, at this point I am awaiting new gaskets for the exhaust, to ensure good seal at the head (I want quiet), and will mount the pipes up with the slightly outboard canting. I'm no longer worried about excessive stress on the head studs, as if anything, this will reduce it compared to stock. This is closer to where they are placed when mounted with the head studs only.
I will either use a spacer on the right hand rear muffler to offset it the same 1/2", or pull and tweak the mounting to hang it in the stock position. The kit calls for tweaking and mounting it in the stock location. I'm leaning towards making a simple offset bracket. Lots of vibration can come through the muffler hanger (weird but true), and I strongly suspect tweaking things so the muffler is pushing hard on the mount will create lots of vibration. But, I'll have to see when I get there after I mount up the exhaust.
The other part is the slight spacing out of the right hand floorboard in order to clear the exhaust pipe. Shouldn't be a bit deal, but we'll see.
At this point, I am not planning to install the electrical interlock that kills the engine if the main transmission is not in neutral and the reverse is engaged. I don't like cutting the main wiring harness. I also don't really see the need. The problem isn't the engine, the problem is the rear wheel is locked when both gears are engaged. I don't fear going into both gears while standing still in a parking lot, it's while riding down the road.
I'd thought about fabricating an electrical or mechanical lockout for the reverse to help better prevent this. But having played with it a little on the stand, I now don't think it really necessary, and suspect it would create more problems then it would solve. While engagement of reverse is simple, it requires a good bit of force, both downward on the shifter and backwards. The reverse slips easily if not fully engaged, with requires a very deliberate rearward motion of the shift lever.
So that's it so far.