Thanks to both of you--fantastic pictures and info! I've attached a picture of the First Generation heater hose nipple for the passenger-side head. Note there is a spiral restrictor inside to limit flow to the heater core.

I've replaced many heater cores in early GTO's due to lack of restriction in the heater coolant feed line (the small hose). I don't want to take off the RF fender on this Firebird to replace a heater core any time soon. If needed, I'll use the same idea we use on early GTO's--a 5/8" diameter cylindrical piece inserted in the hose with a 3/16" hole in the center to limit flow. Meanwhile, I'm going to call Butler to see what they've done with the E-heads.

Also need to figure out where to attach the negative battery terminal to the engine. I hate to remove one of the head bolts to replace with one with a stud to accept the cable, but there may be a better way?