May i ask, what was done with the coolant lines when the carbs were swapped? My 260 had 3 lines from the thermostat vicinity, 1 through the original carbs, 1 through manifold, 1 through balance tube, if i recall. I just put a 4 inch piece of heater hose & plugged the ends with a bolt of appropriate size. (for the carb line, the other 2 i let be) [outlet-hose-bolt]. Recently i've developed a leak in one of the other 2 lines- thought the head gasket went at first, but i just found it with a mirror & light! I may just go ahead and block off all three now. As has been said before, the only downside may be the "coldbloodedness", by eliminating the warm radiator fluid through the intake manifolds. good luck, Jeremiah