67 heads

I just dismantled the 440 in my 67 imp convert, it has 915 heads with 1.60 exhaust valves, plus the smaller combustion chambers, I have a set of 906 heads redone that will replace them. I compared them side by side, could discern no difference in the ports other than the smaller exhaust valve, the external casting is a little different also. I'm going with the 906 heads because of the larger exhaust valve and the larger combustion chambers, which will lower the compression ratio and help reduce my detonation problem.Most hot rodders today prefer the 906 heads. I do however remember 20 some years ago that the 67 heads were desirerable because the small chambers would boost compression and the small chambers gave a more efficient burn, that doesn't apply anymore w/ today's gas.BTW my 67 vert will have a new rebuilt engine installed(plus a rebuilt 727 and radiator too) in a couple of weeks! Can't wait to cruise it!