Techinspector knows a lot more than i do but, Me and several of my buddies run as high as 11:1 on pump gas, high test that is and have no detonation problems, im about 11.2:1 and i have only run high test for 2 years now not a problem, however i wouldnt push the situation, put the 305 heads on and be happy, you will have great bottom end but dont expect it to rev to the moon cause it aint gonna happen, one of my friends has a S-10, 350, 305 heads, very cheap rebuild kit, runs high 14s, its very possible to do this, check out powerhouse engine kits for a cheap rebuild kit, 661-861-0167, good luck