Welcome Ben. I’m in the same boat as far as wiring goes but I’m just going to make a new harness to eliminate the years of the POs wiring headaches and experimentation. I too have been searching for parts and will trust Rock Auto for most of the stuff until I have reason not to. I buy from there all the time for my Audi, Rover, Mustang, etc.. The electrical repros are usually copies of the originals so save some cash there, that’s what I found to be the case when I rewired my 69 Mustang.
I’ve used the listed suppliers on here to get any of the parts that I needed and there is someone in the forum that rebuilds switches.
As far as the exhaust manifolds go I have no idea on warpage hopefully someone else can chime in. I do have a set of 462 MEL manifolds though if you need them. I’m either going 460 / E4Od or Supercharged 5.4L and O.D. trans..
Best of luck to you.