2 things to think of, one is your total timing after all the advance is in shouldn't exceed 36-38 degrees. 45-50 is too much for anything short of Japanese sportbikes.
The octane you should use is largely a function of whatever your compression ratio is. I saw your running 302 heads on a 289 and IF they have larger combustion chambers your compression would be lower allowing you to use the cheaper gas, but pistons, deck height, etc, all affect this. Just use the seat of your pants and run what it likes.
Keep on tuning!
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