Just been sorting out all my aussie 4-speed parts and have noticed something weird.
As far as I knew, bar the input shaft length, input shaft bearing cover length and differing input shaft seals, all aussie 4-speeds are the same physical parts with the following changes to make up the different boxes:

3rd gear different for M20, 21 and 22 (except 6cyl M21 which uses the M20 3rd gear).
Cluster gear different between M20, 21 and 22 plus the specials with odd clusters (XU1, L34).
Input shaft gears different for M20, 21 and 22.
4cyl LH box has a longer (than 6cyl) input shaft bearing cover (must be a clutch related thing).

However, when I was searching the HQ-WB parts catalogues to identify the parts, I noticed that all catalogues list a different reverse gear for 6cyl and V8:

2813525 for 6cyl.
2813500 for 8cyl.

Both engines however share the same reverse idler. I don’t understand what is the difference, or furthermore how there can possibly be a difference. I have about 15 boxes in pieces, and all the reverse gears look the same to me. I know some are V8 boxes by the number of M21 3rd gears and V8 input shaft bearing retainers amongst it all.. Anyone know anything about this??