302 heads smog ports.

I used real small pipe thread plugs. Smaller than the 1/8 pipe plugs that are common on brakes or oil pressure senders. Maybe 1/16 pipe? I am not sure. Drawback is you need to find a pipe tap that size and the plugs. Plus is they stay put. I have early seventies A-body manifolds and the drivers side required a fair amount of clearancing.