Advanced ign cause overheating?

are you using ported vacuum or full time vacuum? when you check the timing is the vacuum advance disconnected and plugged? when you say you have 38 degrees that is all in at 2700 rpm, is that total timing? does the engine overheat at anyother time? or just when the outside temperatures are high?

You didn't say whet you did with the bottom end of the engine, was it rebuilt? If so, when and how many miles are on it? Are you sure the head gaskets are installed front end forward? 16*BTDC is about 4* more than I set mine, but aas long as it's not pinging, it should be OK under load. And with the upgrades you listed (cam and heads) it's now making more HP and burning more fuel than before, that in itself will contribute to the increased heat being generated.

Look at the front corners of the junction of the head & block. There should be a notch there in the head that exposes a corner of the deck surface of the block. That surface, if the gaskets are installed correctly, will be covered by a section of head gasket. If there's nothing but bare deck showing there, the gaskets are backwards and the coolant will shortcut it's way back to the heads and not flowing toward the rear of the block before coming back up to the heads. On a small block, this will cause it to run warm at he very least, and overheat at worst, depending on where the coolant has circulated. On a Cleveland family engine it will overheat everytime and cause coolant geysers due to the coolant ports where it passes back from the heads back to the block being completely blocked. These have only a single port per bank for the coolant to get from the heads back into the block before passing to the thermostat..