It looks like you have everything figured correctly already. The 1958 passenger car 235 should bolt right in, using the truck clutch (bell) housing and the 216 front motor-mount plate. I think that you could also drill your 1958's plate for attachment of the front motor mount.
Also, use your flywheel and clutch assembly, and your original 3-speed should bolt-up fine.
Maybe someone who has done the same thing will respond (and correct anything that I am wrong about).
Good luck,
Tim
