Compression

I have been trying to figure out what the highest compression can be used for regular (87 octane) gas. I have been searching a lot online and get confusing numbers, i have seen some engines with 9:1 compression that require premium while i see others with 9.5:1 that only need regular. Even my dad remembers when he and his friend raced a '68 383 gts in the late 60s early 70s that they could get away with regular, but i think regular had a higher octane rating back then? Anyway sorry to babble on, but im just trying to figure out how high of compression i should have when i finally get close to building my engine. By the way i have a '69 hp 383, but i think i am probably going to get a 360, although i am really no where near these points in my buildup. THanks!