Does it help if you put it in neutral and bring up the revs a bit, to help circulate the coolant? Also , will running your heater/fan wide open help draw heat away from the engine? I know that works with more modern cars. Cranking up the heat when it's 90+ degrees outside is nearly unbearable, but I've done it before!
'68 Firebird, 350-4, 2 spd auto, triple black, Dlx Interior