I have been using Amsoil Dominator 5w-20 in my race engines. The engine builder who built the 360 I just put into my Dart Sport had clearances around .003 all around. I was surprised that oil pressure has been higher than expected, but very good! Even hot after a run, it doesn't go under 40 at idle and not over 80 when warm. Standard volume and pressure pump.

For a dual purpose combo like yours, I'd suggest 10w-30. You want it to circulate as soon as you crank the engine. 20w-50 is just unnecessary. No straight weight oil.

Amsoil high zinc synthetic oil info and variety.