Thansk for the comments and insight, the forum is great for kicking things like this around.
I agree, the HEI is a very tight fit in a first gen. Firebird.
And as I think I said quite clearly
, the choke is locked out / open. With the Performer RPM as you know there is no provision for the heat pick up / mount for the early style choke.
On my 377 Cheby with a large solid lift cam, I don't run a choke, you have to feather it very minimally when you first start it, but from there, no issues with idle / running rich, etc.
Bottom line is that I think the plugs are fouled, and per my discussion with KRE I need to run a hotter plug. This engine with a number of carb config's has fouled plugs from when built, including at Cruising the Coast during a pretty long highway run.