[MrPbody]

Any non-Chevy GM A or F body from '67 through '74 with a will have the "short tail" TH400 (Pontiac calls it "M40"). As long as the trans will bolt up to the engine, and has the short tail, it will fit. You will need the TH400 crossmember for the '67-'69 Firebird. Those are readily available at Performance Years or Ames Performance. And yes, the little TH350 isn't the better choice for the bigger engine. For future reference, most parts (chassis and engine related) that fit the 1st gen Firebird fit the Ventura chassis.

FWIW, Pontiac did not make "biog block" or "small block" engines. If it isn't one of the "bastard" 265/301 short deck blocks, it's a "Pontiac". There are "large journal" and "small journal" blocks. The 421/428/455 uses a 3.25" main journal, where the 400-smaller use a 3" main. But deck height, bore centers, cam-to-crank centers are all the same, '55 through '79, 287 CID to 455....

If you would like more info on making the Poncho nasty, get Jim Hand's book "How to Build Max-performance Pontiac V8s" by SA Designs. This is a very current study of the old Injun and has a vast amount of information on building 10 and 11 second street motors. Chevy guys HATE Chapter 1! (the history of Pontiac V8s in racing)

Jim