In need of some advice whether or not modifications are needed to swap a Saginaw 3 speed to a 4 speed m21 Muncie on a 67 Firebird. ie. bellhousing,driveshaft etc.

earlier m20/m21 bolt right in. 1970's muncie and super t10 have a fine spline input shaft so you need a different clutch disc and the output shaft uses the same yoke as a turbo 400 or 700r4. should be the same length driveshaft. speedo cable on 68 wth muncie comes out above engine and runs down rt. side of trans tunnel. its money in your pocket to buy a trans out of a first gen firebird or camaro so that you get the right shifter instead of having to find another one after. If you pull the trans out and you find that the cover is on the top instead of on the side then pm me and I will buy it from you

sorry I forgot one thing, if your 3 speed was from a 6 cyl the hole in the bellhousing might be a different size. not sure about that part.

Thanks the m21 muncie I have is from a 74 z28 and yes the 3 speed was from a 6 cyl.Does the driveshaft have to be modified?

this link might help because the supert10 is almost the same as an m21. your driveshaft should work but you may need a different u joint http://www.camaros.net/forums/showthread.php?t=98172&page=2

Thanks Neill for all the information it really helped. Cheers!