Who makes flat top pistons for a 260? I thought the stock pistons were a small dish. If those flat top pistons sit .025" in the hole, you actually should be around 9.5 to 1, if they are a true flat top. That SP2P intake should work perfectly with the 500 cfm carb. An 800 cfm Qjet would overwhelm the intake at full throttle, part throttle was amazing. The 450ish GM TBI worked well with it, I could do a one wheel peel with it and pulled fine to the 4200 rpm shift points, idle to 4000 rpm is its rating. Good luck and Thornton Jr manifolds are a nice upgrade for a 260.Flat top pistons so yeah probably 8.5 to 1 or somewhere in there, about the best i was going to get without some domed pistons and i just wasnt going to do that for a play engine.