swapping early 3.09 1st into later case

It worked for me. I bought just the gear-set from Passon Performance and it fit right in. You have to swap the entire set in; all 5 gears.
The gear ratio change is not in the low gear but in the cluster drive;that is, the front part of the cluster and the input gear. AFAIK,ALL A833s have the same First gear.
The 3.09 set makes a great street set cuz you can run 3.55s with them, and the car rockets off the line,like it had 4.12s, with the old 2.66 starter.

I don't get the "masking" business tho..........