Distributor drive gear differences

I was going through my spare parts and realized I have two different distributor drive gears. One is for the later model with the longer length gears then the other is a 40hp drive gear with a short gear. Here is a link to the two I have - the one in the middle and the one on the right.

http://www.thesamba.com/vw/forum/viewtopic.php?t=205262&highlight=distributor+gear+differences

Why were there changes made and can you use the 40hp distributor drive gear with the shorter gears in a rebuild or are the specific to the 40hp drive gear on the crank?

Thanks