It's unlikely that the car and truck bellhousings will have the same motor mount setup. Truck mounts are positioned at a 45 degree angle and use a single bolt through the middle and rubber cushions top and bottom.
You'll need to match up the flywheel tooth count and the starter, but since both vehicles were manufactured with a 12 volt electrical system, that shouldn't be an issue. Chevy trucks changed over to 12 volts in midyear 1955.
If you need to swap bellhousings, the flywheel and clutch will have to be removed, since the flywheel covers up a few bellhousing mounting bolts.
Clutck splines will be identical for both engines.
If you plan to fit a SM 420 4 speed, it has the same bolt pattern as the 3 speed- - - -no problems there.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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