I like Pypes street pro kit, all stainless steel, comes with hardwear, and comes with chambered mufflers, has that flow master sound. It fits reasonably well, needs a little tweaking but most "kits" do anyway.
Start at the tailpipes and work your way up to the engine, trim the 1 foot sections of pipe they give you to make up the difference. Also the long section of pipes that come off the X pipe are too close together and need to be spread apart or the mufflers will be too close to the driveshaft, a...
Not mini tubbed yet but springs moved inboard 3" with the stock gas tank, these are 2 1/2" stainless tailpipes from Pypes modified slightly to fit around the springs
I'll take Chryslers nut and bolt set up any day over Ford and Chevys stud setup that like to break off in the manifold if you don't heat the nuts first.
Moving the column over isn't going to help anything, the coupler is whats hitting the header and the coupler is going to come straight off the input shaft of the steering box no matter where the column is.
Loosen both motor mounts from the block and the K frame, jack the engine up a little then pry the engine over to the passenger side and re tighten everything. There's usually about a 1/4" or more of wiggle room with spool mounts. If it still hits dont be afraid to put a little dent in the pipe...
Put an 18mm spark plug (Ford straight 6) in the bung when you weld it in, this will give you something to hold on to and keep spatter out of the hole. When drilling the hole make sure it big enough to get the tip of the O2 sensor through but not so big that the bung falls through.
Mid 80's M bodies have two small cats on each side up near the manifolds in addition to the one farther down under the floor pan so I don't think the Y pipe is going to fit an A body.
With 2 1/4" pipe by the time you add a few bends (non mandrel bends) it's squeezed down to about 2", as long as the pipe isn't crushed on the bends it is about the right size for a slant 6. Mandrel bent exhaust is overkill for a slant 6. Anything is an improvement over the stock pee-shooter...
That 0 guage wire passing through the firewall is kinda scary, it should have it's own hole with the right sized grommet. I hope there's a fuse between that wire and the battery.
Flux core is fine for exhaust work, like any welding job fit the joints as tight as possable and the cleaner the better. Flux core slag cleans up pretty easily with a wire wheel on a 4" angle grinder. Good luck.
After you get em in take it easy on dips and speedbumps the three tubes under the centerlink hang pretty low and will be the first thing that hits the pavement.