the engime in the 57 can be many different ci displacments .
to rule one of your possible sizes you were told , the 348 valve covers are very different looking than a small block , they look like a " w " shape to them they are the same a 409 engine .
if it is stock it is a 283 , the best way to tell is behind the rear of the drivers cyl head is a casting# on the block , or in front of the pass. head is a flat pad see if there is # stamped there and chase them in a website on engine # . that is a basic way to tell your engine .
to buy a 400 hp crate engine try jegs there are plenty of dealers selling crate motors .
paint jobs are you pay for what you get !!! i start on a paint job for a sand and spray 4500.00
hope that helps you