plug gap, increase or reduce?

Rapid Robert said

I would think that this is a pretty hefty ign (coil/module) & yes that a larger kernel would be a bennie but I've seen several sources (jacobs ign comes to mind) that recommended a smaller gap for power/racing which is confusing. RR

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The advantage of the HEI is that its more capable (or should be) in providing the voltage to jump a more difficult gap and maintain that spark once it begins. It also should be able to adjust the coil current at high rpm. In other words the ignition system should not be a limitation if you want to try .040 or .045" gaps.
For starting point, I'd go with the guys here who have run similar engines to yours in circle track. The combustion chamber, valve events, etc etc are all going to be closest to what you built. We can be pretty sure Jacobs didn't do roundy round with mopar 360s and an HEI.