the 37 flat head block and up had side mounts on the block so i would not call it a hack job the over head engine would be a bolt in at that point the rest hard to say . just about any engine would fit. but i would say away from the caddy flat heads $$$ hard engine to find not hurt or needing alot of work .i would go with a 500 caddy or just about any thing GM would fit like a bbc you have alot to move so you want a big v8 and auto trans like a 4 speed or a 400 3speed with over drive looks like its all there body is solid