Congrats on your purchase, rare find with that milage. Gears are a great place to start off. 3.73 will be perfect for you. Id next start thinking of exhaust or some sort of CAI. Cheap mods....
ive had the headers off countless times, have had no problem with any deformation or warping. Yes the gaskets they gave you are crap, you need to get better ones.
I on the other hand love mac and have never had any problems with any of there exhaust products. I have there longtubes, o/r x and pro dumps and wouldnt trade them for anything.