360 Advice Needed - Autocross / Street Engine Build

There may be other issues but, be aware that you have 2 things that are going to make the coolant hotter:
- Higher CR... peak combustion temps go up a couple hundred degrees.
- AL heads... with their much better heat conduction, the coolant and rad are effectively 'coupled' more tightly to the combustion chamber temps.

As for radiant heat in the engine compartment, those AL heads will also couple the heat into the surrounding air a bit better. Ditto for headers, plus the heat they directly radiate out into the surroundings. Header wrap is partly for that purpose. (The other is to keep more heat in the exhaust and keep up exhaust velocity.)

So you have a bigger heat generator and better heat conduction and radiation all over.

Checking the coolant with a pressure gauge on the rad and looking for pulsing is another thing to do if this persists; the pulsing indicates combustion leakage past the head gasket. There are also chemical based detectors for that issue.