If you can rotate the DM flywheel back and forth more than 5/8 of an inch rather easily, it is on it's way out. Also it will have a vibrating rattle on shut down of the engine. It has a bearing in the center of the flywheel that can go bad, and it will give you a terrible vibrating shake from the tranny while driving. If that is the case, the tranny isn't long for this world, as it will crack the bell housing on the tranny. The conversion kit should be had for less than 1k for the kit. IIRC they run around 675 depending on the kit.
1985 F250 Reg. cab 6.9,94 factory turbo, zf5 speed, 3.55 4X4, flatbed, dual 3.5in. stacks
1990 F350 SRW Crewcab 7.3 turbo 4.10 zf 5spd 4X4
1997 F350 SRW Reg cab powerstroke 4.10, zf5spd 4X4, 3inch downpipe, 6637 mod, intercooler
1996 F350 Crewcab dually 4.10, E4OD, 3" downpipe, 6637 filter
1996 F350 C&C Dually reg cab 4X4 flatbed Zf5 4.10, 3" downpipe, 6637 filter