VW type 1 IRS transaxle differences?

[flyguytilidie]

Trying to order a new transmission for my project. So far it is a hodgepodge of custom aftermarket parts for a pleasure off-road vehicle using 930 axles. So when ordering a new/rebuilt trans, the options are 1969-70, 1971-72, or 1973-79.

Can anybody tell me what the differences are?

thanks