if you have either a C4 or a 3spd behind your six, and you want more gears, why not just go with a t-5 swap out of a foxbody? with the price of a 4spd toploader and that adapter plate, it's probably CHEAPER.
You need an adapter plate, crossmember, and shortened driveshaft (how much or even at all is still under debate), and the tranny itself. I really do think that five gears would cost less than 4 in this case. Remember, if you've got a 6, you can use one of the 2.3 foxbody 5 speeds. they're EVERYWHERE.