OK- - - -the 54 flywheel should have the same number of ring gear teeth as the 216. (139) Chevy didn't change to a 12 volt starter and a 168 tooth flywheel gear until mid-year 55. The bellhousing, clutch, and other parts will be a direct swap. Other than the rear housing, and possibly the output shaft, the transmissions should be the same. The SM-319 overdrive trans is essentially the same as both of your others internally, except for one extra hole in the main case. The Borg-Warner planetary overdrive bolts onto the back of the Chevy case. Your Nova rear axle might work, but it's likely to have a higher speed gear ratio than would be appropriate for an OD trans. An OD in an early pickup works best with a 3.50:1 or lower gear ratio. The Nova will most likely be a 3.08 or so, and you'd only be able to run OD on flat land or downhill.
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!
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