Wow guys!! Funny how a simple question can cause such a fuss, let me provide a little more information of the set up.
When the lower end was returned the from the rebuild shop I installed an Edlebrock Performer top end kit which included the heads, intake, cam, etc. The Performer heads have no cooling ports that connect to the block, they are basically air cooled, The radiator is an aluminum exact replica of the original big block radiator for the GTS, the difference is that the original radiator had 3 - 1/2" core tubes and the new aluminum one has two 1" core tubes. The fan is an original 7 blade with the original fan shroud, the water pump is factory original, the pulleys are aluminum but standard diameter size. The issue occurs after about 20 minutes of very slow moving parade traffic.
View attachment 1715885049
View attachment 1715885050