chevy truck / car bellhousing's HELP please ?

[19673ontree]

hit a snag on this 3spd overdrive , this thing is out of a 1955 chevy , and the front bearing retainer plate is SMALLER in diameter than the 60's one I am used to , one for say a muncie 4spd or saginaw 3 or 4spd is bigger in diameter than this one and you cant swap it for a regular one because the bolt patter won't match ? did chevy make a different bell housing in the 50's ?
I alway's thought that from 1955 to 1967 bell housings were about the same , later they made those big truck bell housings that are even bigger than the ones in our truck's

what to do ?