I know the 89 is a "42" spec'd for the idi's. The powerstroke trans is a "47" spec'd for the PSD. I know the gear ratios are quite a bit different, but the physical dimensions are the same, as well as the bell housings I believe. I don't see why they wouldn't interchange, but i'm sure someone will chime in with yes or no.
I do know that i've "heard" that they won't. But that was from an uppity powerstroke guy who thought every other truck in the world was a piece of crap except his.
I also know that the "47" trans from the PSD is quite a bit "rarer" since it was only made for technically 3 years 95-97, meaning around here in the south it commands a much higher price than one from an IDI-sometimes double. That coupled with the fact that almost every one i've seen used for sale around here has either 3rd, 5th, or reverse chunked out of it due to the redneck sled pulling circuit in these parts. ASK me how i know................