Transmission problem

[Drifter]

I'm new to the Subaru world and recently bought a 1992 SVX LS-L and
My transmission is slipping 2nd to 3rd and I believe 4th to Over drive.
I'm considering to rebuild or or put in a used tranny.

Looking to rebuild myself, though it would be my first rebuild or I would install an Automatic or possibly a Manual (used) transmission?

Does anyone have any advice on the most ecomical way to go about my repair or replacement?

PS; I have also noticed that the rear wheels don't seem to be working... it seems to be FWD mode?

Thanks very much for your time?