Hopefully you also got the trans. that goes along with the '61/401. Swap bell housings & torque converters from the '61 to the '54 & you should be good to go. Even better would be to change the '61 DynaFlow to torque tube end & have a much better trans. with a variable pitch torque converter. Hopefully the car this stuff came out of is still available for linkages that are needed for the trans. Strip the rubber from the '61 mounts on the engine of the '61 & bolt the engine brackets from the '54 on. That takes care of the mounts. Everything else is just about a bolt-in.
Tom T.