Need info/help on a 340

I have more information. The engine is stock bore, stock stroke, stock pistons and stock deck. It has j heads with 2.02 valves and 3-angle valves. Why on earth would this thing be running 100 octane? Shouldn't it be 8.5-1 compression it's a 73.

You should be able to run it on regular pump gas. 87 89 octane.