well i went to the dyno shop earlier this year and was surprised to see that my 65 only put down 213hp and 268trq to the rear wheels. desktop dyno sugested 320 at the flywheel, working backwards from my dyno numbers im at about 284hp flywheel with a 25% drivetrain loss. (its a C4 and 8") i think some of it has to do with it running a little rich. and some of it i'm sure is due to the restrictive heads. i'm running 68 302 heads with 1.94/1.50 valves. Roller rockers & screw in studs w/ guide plates but no port work or any other tricks. i have a crane powermax272 cam it is a split duration cam 216/228 and .484/.512. its nice but i believe the heads are restricting the top end. i am considering the AFR185's for repalcement but i am not sure if those are too big and maybe i should go with the AFR165's? if i plan to build the 347 i think the 185's will be better but i wonder how much the torque will suffer if i put them on my 306. anyone using either of these heads? if so i could use some advice, thanks.