I know that there are posts on this but I cant find any that specifically answer my question. I am looking at doing a 500 EFI build for a new project. I have everything to build one except the lower end. So my question is what is the difference in a 500 EFI long block vs a GM ZZ 502 long block. I know the oil pan, cam and heads but are there any difference in any of the internals or clearances for the internals? Thanks in advance for any help.

I would be willing to bet that the ZZ 502 is tighter if original. The ZZ 502 also has aluminum oval port heads that wont match your rectangular port 500 EFI intake manifold.

I am running a modified version of the ZZ 502 with marine tolerances on the short block and Stainless/Inconel valves. It runs good, but the 110cc heads make a lot of heat. I am keeping plenty of fuel in it.

If you are paying anywhere close to retail for the ZZ 502, I would consider this instead.
http://www.high-performance-engines....ine-p/hp95.htm