if your looking to make it hold up to a bit of extra power and some abuse i would suggest maybe just buying yourself a complete overhaul kit from
Home with the upgraded mainshaft
They have complete kits(not cheap), including the mainshaft (so you can swap out to a 4x4 shaft), plus they also sell the 4x4 tail housing (not cheap)
But its not going to be cheap...
If your looking for cheap, i would suggest you keep looking elsewhere for a 4x4 trans. either to use as a complete unit, or for the needed parts.
Depending on how much the guy wants for the 94, i would say you might be best off passing on the deal. It might end up costing you more to convert that trans, than it would to just pick up a 4x4 trans (not to mention that 4x4 trans would likely have your needed tcase/shaft behind it also!)