New to me 67 Chev 1 ton

It has a clunky 4 speed and low rear gears, is there a modern manual trans with overdrive that fits that bellhousing?

Its getting a disc brake front end, power steering, sway bars and hydroboost.

And EFI if I can find a manifold.

I don't know of any modern trans that will go into the bellhousing you have now. Your truck may have either an NP435 or an SM465. To differentiate, the 435 only has one PTO plate and the 465 has one on each side so crawl under there and count the pto plates.. The NP435 and SM465 also use different size register bores in the bellhousing so even swapping one for the other isn't easy. It's academic though as neither have overdrive so the best scenario is to remove it and sell it to the rock crawler dudes. The main issue with swapping to later type of trans is that the rear engine mounts on your truck are on pads built into the bellhousing.

You best option is to remove the existing center crossmember where the rear mounts are. It is riveted in from the factory and it's annoying to remove. Then once you have the center crossmember removed you can install a modern trans and bellhousing and use a normal crossmember under the tail of the trans. I have done it that way a few times. The NV4500 is a good option for a later model trans swap. 

Your rearend will be an Eaton HO72. You have no good options for modern gearing there aside from swapping to a later model cab and chassis 14 bolt axle. Remember, your truck is not a dually. It is a cab and chassis. The difference between the two rear ends is about 18 inches in width so, big deal to understand. 

Probably not something that fits the removable bellhousing, but if it's a typical chevy V8 I think the NV4500 is what the newer trucks would have come with. Look for one out of a GMT400 2500 or 3500. The 1500s got the NV3500 which is a decent trans, but not up to 1-ton duty.  There's a Chevy-pattern ZF6 out there as well, but it's pretty rare. 

Rock crawler dudes quit using manuals 20 years ago 

I've sold several SM465s to rock crawler dudes in recent times. I assure you they haven't all gone to automatics. 

In reply to Cousin_Eddie (Forum Supporter) :

Thanks for that rear axle reminder!  I have a narrow axle @ 84" to outsides, vs 92" for the dually axle (which will not fit my flat bed).

Power steering upgrade looks like the big challenge.

Any recommendations? It has servo-assist.

Can I notch the frame? do I need to?

I actually wrote this article but Photobucket has messed up the pictures. If you read down though, other dudes posted pictures and info. Short answer is Rez Engineering bracket. They still sell them for your 67 model through Facebook if you will contact them.

Article on converting early trucks to common power steering box.

Which is cheaper to buy; a transmission or another rear end?  Ever swap gears before?

The HO72 doesn't offer you any option friendlier than 4:10 if you're looking for highway driving. Also the HO72 is obsolete as far as service parts go. I haven't had one in 15 years, and even then I couldn't find brake parts. 

The square body cab and chassis rearend is a 14 bolt and it offers you a wide variety of ratios to choose from, some of them downright highway friendly. Also unlimited service parts to keep it alive and happy no matter what happens.

In reply to Cousin_Eddie (Forum Supporter) :

Yeah I rebuilt a HO72 many years back back and had problems finding parts.

The third pinion bearing had come apart.

It's pricey but there's the new TR4050 that can be had with a Gen1 SBC bellhousing.