Question about a trans I have.

Rear timing, Okay, gotcha. They used that for timing the motor at the bellhousing from the doghouse on RV's--hence the hole in top.

As for additional case strength, etc., all the 727 cases are pretty much the same and no reinforcement was done over the years until they got into the 518/618 4 speed automatic. Extension housings were different, however, as the side snap ring access cover housings had additional strength over the extension housing with the bottom snap ring access.

Hope this helps ..