Pre 99 solid axles will be 1.5" shorter overall.
Try and find a 99+.
I can't be much help because I purchased everything new. From what I've read, it's pretty much a straight up swap. Everything will just bolt right up. You will have to swap out the axles (of course), the catback exhaust, driveshaft, and e-brake cables. That's pretty much it. Oh, and of course the springs and shocks.
Nope, all are 28 spline as far as I know.
I purchased a new 99+ Ford carrier and the shop replaced all the internals...31 spline mosier axles, 31 spline eaton diff, 4.30 gears, svo UCA and mega bite Jr. LCA's, ect....
As for the intake work, the guy no longer does it anymore. There are a few people over on www.blueovalnews.com and www.corral.net that I hear do this work now. I don't know their names though. If you want to spend $600 you can have www.extrudehone.com do the intake for you. Or if you plan on staying n/a and have money to burn there's the FR500 option.
whats up man i have a 99 cob and i replace my rear end to a solid with 456 gears its nicer and stronger i suggers an alumm. drive shaft for some reason my vibrated alot i changed the drive shaft and prob fixed, it took my a lift and 5 hours and i changed mine good luck