Which transmission do you have? Isn't the '47 4-speed the old crashbox version regardless of wether you have an Art Deco or an Advance Design? If so the later bellhousing that fits the motor you want to use won't fit the transmission. You need an SM420 which was used '48 to 60-something instead.
If it currently has a 235 in it someone swapped the motor, and may have already updated the transmission.
