New Old 53,
46forme is correct about the intake/exhaust manifold for the 216 not fitting the 54 or later 235. It might be possible to use the 235 intake manifold mated up to the 235 exhaust manifold. Maybe some else will comment on this possibility.
I am pretty certain that the 1954 motor mounts are different from the 1953. You would have to use the 1953 bell housing and motor mounts (I think the swap is straight-forward - the flywheels have to come off in order to remove the bell housings). The '54 motor mounts allowed for no transmission mount (and cross member), so you should also use the '53 transmission mount (if it is stil on your '53 transmission).
If I am incorrect with my advice, you can bet that corrections will follow. You should find the '54 235 to be noticeably more powerful than the worn-out 216.
Good luck,
Tim
