How do 47-54 frames differ from 55-59 in regards to motor mounts?

[Matt300ZXT]

I'm stuck with this dilemma of making this car 235 work in my truck or just dropping in a dirt cheap 305 or something. It's a 54 1/2 ton and I'm curious if the frame rails/widths are so different 1 year apart in the 55-59 style, that a motor mount like this would/wouldn't work?



I know there's the old faithful universal crossmember style, just curious why something like this wouldn't be available in a store's 47-54 section.