I haven't revisited this thread for a while, but I have mine all apart and plan on putting it all back together tomorrow. Here is what I have found through extensive searching, reading, looking at clutch catalog, buying and returning parts, talking to clutch guys, etc. etc. etc....
First, comparisons between the T-19 and the ZF: I was told that the T-19 and ZF-5 bellhousings were different - that the ZF was deeper. Then I set them side by side and started taking measurements and all the dimensions were essentially the same. So that left me sratching my head wondering how they made up for the difference in the thickness of the two flywheels.
I happened to have the DMF that came with the ZF-5 I bought, so I pulled the SMF off my truck set them side-by-side. Then I got 2 standard clutch sets - 1 for the 6.9/T-19 with the SMF and one for the 6.9/ZF-5 with the DMF and started comparing them. With the pressure plates on the flywheels the two assemblies were the same overall thickness.
BUT when I set the DMF pressure plate on the SMF, the overall thickness of the whole assembly was 1/2" less. Comparing the two pressure plates it was immediately obvious that the SMF unit was thicker (deeper?) than the DMF unit to make up for the difference in the thickness of the two flywheels. The DMF pressure plate would bolt right up to the T-19 SMF - they both have the same 2-bolt on 3 pattern. The problem is that if you bolt the DMF pressure plate to the SMF your TOB has to move 1/2" farther forward before it even contacts the release fingers of the pressure plate. That means the geometry of the TOB fork all out of whack and you have to modify it to make it work right.
Second - they offered both 11" and 12" clutches for both flywheels, and the input shafts of the two trannys are different. The T-19 shaft is actually 1-1/16" diameter and the ZF is 1-1/4". The biggest problem with doing the conversion is that both sizes of DMF clutch disks came with a solid center hub. That works if you're using it with a DMF which has its own springs to absorb the shock loads. It won't work so well with a SMF - that's why their clutch disks have springs in the center hub - and pairing the SMF with a solid center clutch disk means there are no springs anywhere to absorb any of the shock load.
Third - the crossmembers (at least for the 4x4 uperCab) are compatible. The T-19 and the ZF tranny mount are the same, and they are very close to being in the same location. The ZF mount is approximately 1" farther from the front edge of its bellhousing than the mount on the T-19. HOWEVER, the frame holes for the crossmember allow for about 1/2" of movement forwards or backwards. Even more important, the holes in the crossmember itself where the tranny mount sits are actually slotted and allow for at least an inch to an inch and a half forward-backward adjustment. The T-19 mount bolts sat at the front of the slots, and I'm pretty confident that when I go to put it back in tomorrow that the ZF mount bolts will sit near the back of the slots.
So the big problem I faced was to find somewhere I could buy one of the deeper style pressure plates for an SMF, AND a clutch disk with springs in the hub that will fit the 1-1/4" input shaft of the ZF.
I have only been able to find ONE manufacturer of "regular" (i.e. inexpensive) ZF/DMF clutch disks who puts springs in the center hub - just like the T-19/SMF clutch disk. That manufacturer is Fenco. I have also only been able to find one place that sells these two components separately instead of as part of a kit. Autozone sells the pressure plate under the ValueCraft brand part # CA31055. They sell the clutch disk under the ValueCraft brand as part # CP31103A
The only drawback is that these are the "standard" 11-inch clutch components rather than the "HD" 12-inch setup. HOWEVER, the clutch, pressure plate, TOB, and pilot bushing all added together cost me only $184 with shipping. Compared to the 12" LUK flywheel & clutch set for close to $600.
The best thing is that these are all standard components that can be replaced or rebuilt the next time its needed - instead of being a custom LUK replacement disk & pressure plate - which cost about $350 even without a new flywheel.