383 rebuild - kinda whimpy on the dyno?

I remember seeing some flow tests on iron heads with porting and valve work, but I don't remember were from. Simply adding 2.14 1.81 valves into decent stock iron head without any other chamber or port work reduced mid lift to peak flow down to near the level of the old pre 1967 closed chamber 516 heads. Even if you have to do it yourself, porting with a set of MP templates will help immensely. Looks like you need to change to heavier valve springs anyway, so it would be a good time to do it. At least the cam is broken in and that is less of a worry ,but if you've got it out anyway, it's still best to treat it like a new one and use break in lube when switching to heavier springs.