OK, didn’t realize the reed blocks were different…Perhaps the 50hp uses the shims. The marineengine breakdowns are a little lacking, there is no explanation for all those little numbered notes. The difference between the 40-50hp crankcases might be nothing more than a silly little water spray into the exhaust cavity. Again, these engines are so "over engineered", and not in a good way. "Exhaust tuning" is relied on for some of the WOT power and mid range running characteristics. The sync procedures are so overdone as well, the 1988 models are easy to sync up, 89 and newer ones involve a long/drawn out procedure that can be confusing and easy to mix up.
So, in this case, I would just go ahead and do the sync procedure, I don’t think the different sized intermediate air bleeds are going to make much of any difference at all…