MK 3 timing cover screws........

Hi, just a simple question, why are they longer (1" -1/4) comparing to the mixed pre MK3 ( seven are 1"-1/8,one is 1"-1/4,and the four short at 1"), so is it cause of the timing cover or the case........???

The depths of the screw holes in the Mk3 timing cover appear to match those of the pre-Mk3 cover so it seems to be the crankcase.

My '72 screws are the identical length; I just bought stainless allen head screws for $4..... Seems to be some history here.