Jim, that's certainly an option, as long as the gasket/seal is tight. It doesn't take much to compromise the seal, sometimes I have to silicone around intake bolts, etc.
There are some pictures floating around of a bunch of Tunnel Port crate engines at Holman Moody's shop and all of them have chrome PBF valve covers with the big cookie cutter oil caps. So, I think I'll try one of the cookie cutter caps or a cap like you specified first and see where that puts me. If it doesn't work, I'll probably hit Tindle up for some MT covers.