There have been several who have converted over to the ZF-6. I don't know anyone who has switched over to a ZF-5 except down in the OBS section. There should be no reason you couldn't do it. I believe the ZF-5 is a smaller tranny, so you may be able to get away without modding the floor pan hump as is required for the ZF-6. You'll also have to get a custom front driveshaft since the 5 is shorter, but that part is easy.

You might also ask this question down in the 94 - 97 diesel section since they have more experience with the ZF-5