i got a used engine for my car from a 1999 buick lesabre. i thought that i had switched everything i needed to (sensors, mounts, etc.), but the header doesn't fit into my current exhaust system. The studs on the buick header are farther apart than the holes on my current exhaust mount bracket thing. so my question is do i have to swap the header with my old one? can i drill/cut new holes into my current exhaust mount to make it fit?
also, the holes in the flexplate don't quite line up with the TC. I can two of them in solidly and straight, but one of them won't go in straight...or go in at all. do i have to install my old flexplate also? i really don't want to pull the motor again, i just want to get it running.......

Nick, I don't have any answers for you other than to ask whether you have looked at the rear exhaust manifold on the LeSabre to see if it will clear and attach to you cross-over and downpipe. If so, then that may be your best bet there. Or use the complete Lesabre exhaust all the way to the downpipe connection.

Other than that, a free bump to give this exposure to someone who knows more than I.

Swap the manifolds. If you don't, other things may not line up either. Do it right and you'll finish quicker.

BTW.. using a Buick is rough..you swapped almost everything on it..

well, i found out i had the flexplate wrong, and i tried again and it worked, so it'* bolted to the TC, which is good....we're just gonna drop the whole exhaust and grind the holes out a little bit more so that the current mount will fit on the header, cuz the pipes themselves are the same size. but thank you for the responses, swapping the parts wasn't too bad