I think the 68 4 speed cam is not much bigger at all the 284 vs the 268 is not even close to a modern 284 vs 268, and the lift is about the same anyway. The 71 carb and intake to me is a bigger plus, this is the big reason the 71 a body Is the year to use in F.A.S.T. Racing. And even stock. The only thing missing was a 68 383 roadrunner beat down!