If you build the 400 correctly with the steam holes in the heads you wont have any problem. This was a problem about 20 years ago, when we did not know to much. The 400 was made to be a truck motor and run at 3000 RPM. Then it was revised for cars.
In the Knowledge Base there are numerous postings to this subject on hot to fix it from heating up.
In traffic like cruising Woodward, 18 mi. long, takes about 1 mile an hour and mostly idling, my car went all the way up to 185*, again its all in the blueprinting of the engine, this is a 427 small block, mechanical pump, thermo clutch fan and stock radiator.
Just have to do a little reading like the one site from grapeape, and the KB has plenty sites.
Luv the smell of NITRO in the morning.