Lots of interesting opinions here.

I have personally seen a professional engine rebuilding shop in my neighborhood lift complete (with accessories) big block V8 engines with "carburetor plates" fastned to aluminum manifolds with 5/16" bolts on a regular basis. They tell me they've never had a problem with that.

I'd never try that. There are to many available 3/8" and bigger threaded holes in the heads and blocks to trust a 5/16' hole threaded in aluminum.

Ray