Welding dissimilar metals on an exhaust

I've been reading up on this, but would like to see if anyone has personal experience.  I have a set of 304 stainless headers going on my project.  I have the cats and some of the pipe from the donor vehicle, which I am assuming is 409 stainless since it is OEM, and hasn't rusted to nothing after 20 years in Ohio.  I am not sure I want to make an entire custom exhaust out of stainless, ue to cost and availability issues right now.  I am thinking of making the exhaust from the headers to the cats 409, then just using regular steel after the cats.

1.  I've gotten the impression that welding 304 to regular carbon steel is pretty much a no go, but 409 can be done.  Is this correct?
2.  If #1 is correct, it looks like I can use 309L wire with my 75/25 gas combo to weld 304 and 409 stainless together.  Can the same be done for 409 to steel, or do I need to switch back to normal MIG wire.
3.  As a way around some of these issues, I've also thought about going with V-bands, at least at the joint between the 409 and steel section.  Would this make sense to do?  I assume I'd just need to find v-bands that match the material I am welding them to.  I have not really researched this, so don't even know if I can get them in carbon steel.

I'm very much an amateur welder, no experience with 300 series stainless, but I have partial answers for 2 and 3. I've had great results welding 409 to mild steel using normal mig wire and 75/25 gas. The 409 seems to take a little more heat, so I favor that side of the puddle a bit with the arc and let the heat from the puddle flow into the mild steel. These welds came out as good as anything I've done on mild steel and have held up to all kinds of heat and stress for the past few years (v-banded downpipe-to-cat sections on a turbo setup).

You can get mild steel V-bands, but most of the ones I've found are zinc plated, which is incredibly annoying, because you want to remove the zinc from the area you're going to weld, and then the heat from the weld makes most of the rest of the zinc peel and flake off anyway, so what was the point?

I'd just run 309 on everything if you have it.  It plays fine with mild steel in my experience.

Heck I've had success with regular old er70s-6 on 300 series.  

I've welded plain steel to stainless on my racecar exhaust with just normal mig wire and never had an issue.  

The heat affected zone on the stainless will no longer be stainless (it will rust), but if you are welding it to plain steel, that doesn't really matter anyway.

I have always just used good old ER70S6 when welding mild to stainless.  Or stainless to stainless.  It actually welds easier than stainless wire, which I have found to be nothing but finicky.  Not fun when already dealing with a finicky material.

Stainless driver side exit Y pipe I made out of stainless mandrel bends and other bits and bobs, and the original Y pipe, all with ER70S6.  Works just fine.

I welded 316 to carbon steel and it worked fine. You lose the corrosion resistance at the weld, but that's understood.

It is sounding like I've been overthinking this.

Or avoid the weld and run a butt clamp if you're worried about it

Shavarsh said:

Or avoid the weld and run a butt clamp if you're worried about it

The farther back part may work that way, but up near the headers I want as leak free of joints as possible, and a crossover on the drivers header to the passenger side with very little clearance.

I've welded 300 series stainless together but never tried mixing it with mild steel.  If you use stainless wire for a more rust resistant joint, you're supposed to use the tri-mix gas that is crazy expensive.  I just use mostly argon and trickle in some 75/25 gas to cool the puddle a bit.  Works fine and I already have pure argon for welding aluminum.