[hemigremmy]

My car was doing a similar thing after i changed the motor (SBC .030 over) out to a freshly rebuilt one that was nearly identical to the one i took out. It ended up being that my air/fuel mix screws wern't backed out enough making the car run lean when driving. At idle in the driveway it would run 180-185 all day long with the fan cycling, take it out on the road and just drive it, not getting on it really and it would be up to around 220. I backed the screws out another half turn and it seems to run good around 190-195 now.
Check that

[Houston54]

Thoughts that came to my mind on this were:
Waterpump rotation? Is the pully set up different than stock? Water pump maybe a reverse rotation version? Cooling system bleed to remove air?

I am running a SBC in a 54 Chevy truck with a 3 row desert cooler radiator on which I have installed a Ford Taurus 2 speed shrouded e-fan that is controlled by a Derale adjustable temp controller with integrated relay and fuse. I do not have AC on the truck yet but this set up keeps the temp at 180 in Houston traffic. The high speed on the fan will be wired to the AC compressor. Hope you solve the problem.