I'm no guru but I have discovered that
there are three 904 style transmissions; the A904, the A999, and the A998.
AFAIK the A999 has always been a loc-up with the 2.74-1.54-1.00 ratios.
AFAIK, the A904 was never a loc-up, and always had the 2.45-1.45-1.00 ratios.
AFAIK, the A998 could be had either or; that is to say, could have had either gear ratio and could be had with or without a loc-up.
The lock-up in the early years was hydraulically controlled. In later years it was electrically controlled.
So
If your case has provision for electrical loc-up, and you need it, then you can only use another case that has the same provision.
But
If you have a hydraulically operated loc-up, then you should be able to use any 904 case.
I noticed some differences over the years around the accumulator, in the routing and shapes of various passages. I do NOT know if this will be an issue. If your broken-one and your swap-candidate are the same in this area, then I would swap the guts and air-test it. If it passes the airtest, then the VB should also work. so long as both cases are for use by the same loc-up activation method.
Either gear ratio can be swapped into either box.
BTW
that case is aluminum, as you know, and easy to weld up.
