Would like some ideas on what to use to plug the hole behind the intake where the internal breather is. I'm putting a newer intake and valve covers with breathers on it. Thanks, Kevin

A freeze plug of the correct size should do the trick.

you may find a ventilator canister under the intake, thats where a lot of people remove and install the freeze plug there. but putting a freeze plug in the opening under the distributor is ok too or both if you like,