Well it is a 65 389, but the heads there are no XXXXXX877 there is a XXXXXX8177 or a 77. I am guessing they are 77 since that would make them 65. made 360 from the factory ongood leaded gas.( cr should be 10.5 ) So your going to have to run something better then 91 octane... AS it sits now with the logs and the tripower( witch actaully hurts the prefromance if you want to do upgrades latter) i am guessing it will make around 350 if its in factory trim, or about 375 if its been roded a little.