There are several differences between the two.
MkII's normally have a flat dial and standard Speedmaster dials are not flat
The two cases and movements often have different lengths of pins for the pushers, so no guarantee that fitting one into the other will work, without some modification.
The movement holders are obviously different for the two types of cases, and also the method of fixing the movement to the case. But just using the correct movement holder for the case should be fine.
Your best bet would be to buy a good normal Speedmaster and fit it with the dial and hands from a MkII Racing. The movement may sit slightly further back from the front of the case since the MkII dial is flat and the normal Speedmasters are normally curved. I'm not sure how much the difference is but I've seen MkII dials fitted to standard Speedmaster cases so I'm assuming they fit.
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