[Tommy]

A temperature of 115/120 C at a standstill seems the fundamental problem to me. Since it runs at a much cooler 70 C on the road, I suggest you check two things first. One is the air flow over the radiator. For example, if you are using a puller fan (aft of the radiator), be sure there is a shroud that directs the air through the radiator before it goes through the fan. The other thing is the timing at idle. I suggest you put a timing light on the engine at idle, then remove the vacuum line to the distributor and cover the hose (to prevent a leak). If your vacuum can was working correctly, you should see the timing advance (e.g., from 5 degrees BTDC to 12 degrees BTDC). If you don't see the advance, that may also be contributing to your overheating at idle.