Originally Posted by wstar

Well it's 3 lines really, but the true bypass is 5/8", the heater is 3/4", and then there's the throttle body line that's more like 5/16". I'm guessing the thermostat closes the true bypass as it opens the radiator flow path, but the heater line remains open full-time? In either case, I suppose a machine shop could make an adapter plate that goes on the side of the engine there and connects one or both ports to a single AN fitting like Spohn's pic.

I really don't think the car needs gargantuan amounts of bypass flow anyways, just to keep from boiling fluid in the heads till the thermo opens up. I still kinda think you could get away with a thermostat-only solution, too, though. Close off the heater/bypass lines completely, and install a modified thermostat that allows sufficient "bypass" through the radiator even when "closed" (by drilling out the plate that closes it a bit - it already has a tiny hole in it, just needs a bigger one).