The big block/small block mount question has an easy answer that could be wrong.
The mounts are the same.
But because the physical dimensions of the big block are different you may find that a location that worked for a small block won't for a big block.
Take your question over to the Hi Po forum and ask about a big block in a '55 (1st or 2nd as appropriate). Someone will know how it fits.
You use a 396 as an example. If you have the motor trial fit it...
