I have some Q's about an 89 2500 454/TH400 suburban, just purchased, and want to repair some things so itll be as durable a tow rig as possible. I has some oil leaks, the one I am primarily concerned with is the rear main, is it one piece??? It also leaks from the front and rear of the intake, so Ill pull it as well. Any performance ideas as to intake besides that expensive ass Edlebrock manifold?? That big ass TBI appears to have a bolt pattern the same as a square bore carb????(I wanna keep the air injection and EGR for emmissions regs). I also found a broken bolt, rearmost exhaust, passenger side, obviously contributing to my exhaust problem, andy tricks on drillin that one out, its kinda tight back there!!! It seems to be 2 threads in, and Im not reassembling it to hear it leak again!!!! Any tips would be helpful, had this thing for about 3 weeks now, soits new to me.

Well if you still have the original 89 block... Mark IV 454 lasted till 91 and have the 2 pc. rear main. Mark V's began in 92 and some aftermarket blocks and were the first to sport the one piece rear main on a BBC. The easiest way to tell if it is still a Mark IV is look for the mechanical fuel boss. IV's had it.... Mark V's didn't.

Manifold wise... I don't think it is worth just upgrading the intake... if you were doing heads, cam, and intake yeah, but just and intake won't do much for that motor IMO.

Not sure what the deal is on your busted bolt issue... I would say pull off the maifold and try and heat it up with a acetyl/oxy setup and turning it out with a vise grips or possibly an easy out if you have no stud left to work with. If that doesn't work I would just drill it out carefully and Heli-coil it. Good luck.