Proper ignition timing?

[chiggins]

So here's some background info: (I'm not at all experienced here so bear with me) truck has got a frankensteined 307 in it, year unknown but I'm guessing its about a '71. I installed a mild summit truck cam and swapped some heads off of a mid 90's tbi 350. The cam specs are Duration 278/288, Lift .421/.444, and the different heads brought the compression to about 9.8:1 I believe. it has a brand new HEI system and a 600 cfm edelbrock
So with this info in mind, where would someone advise to have the timing set at? turns out when I set it, I put it at about 24 degrees base timing, which I know is too high, but the truck was running fine. Problem is, theres a slight ping at higher rpm's when running just 87 octane fuel, and no noticable ping when running 93. But then dropping it back down to 16 degrees like a typical engine should have it's a total dog. Would setting it to about 20 be a decent idea? do I have to accept the fact that having a near 10:1 compression simply isn't driveable without higher octane?