To me there are three kinds of transmission work for these cars, what I can do myself, replacement from a yard (provided I can examine the car it came from), and replacement with a factory remanufactured transmission. In the case of an 87-89, the remaned trans is brought up to the latest specs for the 4T60 (and there were a *lot* of slipstreamed improvements - just read the TSBs).
AT work is a specialty unto itself and requires special tools to go deep inside. While I have rebuilt a blown manual trans on the back of a trailer, automatics are a different breed and given the difficulty of R&R, would prefer to know it is right before it goes in.
BTW I see several more 4T60 ratios, in all : 2.73(FP3), 2.84 (F17), 2.93 (GW9), 2.97(F79), 3.06 (FW2), 3.33(GX3).
BTW2 if you want a 3.33, just look for a Grand Prix or 6000 or equivalent Chevvy, etc. with 2.8l engine and o/d trans..