Buffalo makes you a flex plate with the adapter. You need a '75 or so starter to bolt to the adapter. A '55.1 should already have an enclosed driveline with 3.90 gears. That will be adequate. A universal crossmember will work. You will have some cutting to do on the floor. If you can find a floor pan from a Hydra-Matic truck, cut the floor to fit it. You won't be able to use an SM420 shifter on an automatic but there are aftermarket floor shifters. Keeping the clutch pedal in place sounds pretty goofy to me. Yes there is a 4 bbl intake made but I'd go with 2 Zeniths.
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