Best Fuel Option

Let me start by redescribing my combination: 73 based 318, stock bottom end, rebuilt heads, hardened seats, stock compression replacement pistons, stock head gasket thickness, Comp XE268 cam, .477/.480 lift @ .050, matching springs, Hooker headers, Edelbrock performer intake, 600 CFM eddie manual choke carb, dual snorkel. mid seventies style air cleaner with stock replacement element.

904 trans with TF2, stock verter, 2.76 7.25 rear.

What is the grade of fuel that I should be running? Is 87 ok, due to the still lower compression, or should I run 89? I have 10* of initial timing at idle and there is no pinging. This is with 89.

Also, Im guessing 260-270 horse at the crank, does this seem like a fair estimate?