Either would be perfect, but unless the .021" gaskets are easy to get I would opt for the more readily available FelPro, IF the FelPros would hold up to 13:1 CR & nitrous.
The gaskets I have in stock are the OEM steel shim gasket (part number 2843182). They do mic between 3.510-3.515. I have my doubts about either the Felpro or the OEM steel gasket holding up to 13-1 and nitrous. I would opt for a solid copper gasket with "O" ring in the block and/or head.
