It's a 904 trans.
Good question. Maybe someone will know for sure.
I'm thinking on one hand the stock trans will shift softer and slower so, if the frictions are worn and glazed, it might last a awhile.
On the other hand, putting in the shift kit will quicken the shifts, putting a load on the frictions the instant the gear changes, increasing the chance of slipping. But the kit increases line pressure some
You can change the 2nd gear band apply rocker arm so it will shift quicker AND hold harder.....so I say GO FOR IT!
Put the shift kit in and adjust it for the [strip] mode and tell your Mom to hold on to her dentures
when she drives it to the Rite Aid for her prescriptions!