Firebird Cadi swap

My brother owns a 1970 Cadillac Sedan Deville with a 472 ci engine. His transmission blew this past summer. I was wondering if the th400 on my 1969 firebird would bolt right on to his engine. Were thinking about making this swap so i can put a muncie 4 speed in the firebird. Also is this swap worth the money/effort? We were figuring either way we are spending a good amount of money on a new transmission to go into his car.
The shop manual says something about a THM1 as a label for the transmission, but i thought they still ran with on a th400.

Bill,

The bellhousing pattern and trans mount are in the same spot as the M-40 (Pontiac's designation for TH400). If the tail housing on your Cad is less than 6" long, then it should "bolt right in". If it has the "long tail" version (the Cad, as the F-body is most certainly the "short tail"), it will still fit, but you must either get a new driveshaft (longer to fit the Cad) OR take the trans apart and put the output shaft and tail housing from the Cad into the Pontiac. You may also take a close look at the splines and diameter of the output shaft. There are a couple variations on the theme...

Jim

So Im going to go ahead with the swap, and ive got a transmission being shipped over. I think im going to have everything except the bellhousing and the flywheel. Before purchasing im trying to find out if theres a difference between the 10" and 12" flywheel, because ive seen both out there for 69s. My main question is will all bellhouses fit either flywheel, or do some housings only fit the 10". Is the only main functional difference that the 12" would have more torque, and the 10" would be more top end? Also wondering if the gear tooth sizes are different, so that only certain flywheels match up to certain engines(crank?).

There's no difference in the diameter of the 10.4" clutch or 11" clutch flywheel. There is no 12" clutch for the Pontiac. In '69, only the 10.4 was in Firebirds. The 11" job came only on "big cars" with the 428 engine. The difference between the flywheels is strictly the bolt "circle".

There are a couple of flywheel "weights". We've seen both 30 and 40 lb. versions from Pontiac. For the lighter car, the 30 lb. unit is desired.

Chevrolet, Olds, Buick parts WILL NOT FIT. The Olds and Buick bell housings will fit the engine, but they must have the starter recess on BOTH sides. Pontiacs have the starter on the dirver's (left) side.

Jim