Typically it's more involved than just an engine swap as teh Torque converter locks up and stalls at differnt times between gas and diesel. I know it took a lot of time to Square daves away because he kept the stock ZF torque converter etc.
Thanks Shop Boy for the plug
We reused my '97 ZF (your ZF needs to be the hydraulic type, not a later model electronic), and 1:2 TC. The "time" taken to square away things was really spent on modifying the brackets sent to retorfit the 2.8 to the NAS V8 frame, and to adjust kickdown and throttle to get things right. Sounds trivial but they ate up time, plain and simple.
You can get away with reusing the v8 ZF but the shift patterns are a little chunky. But, knowing now, what I did not know at the time. You can buy the proper ZF governor $100-300 for the tdi and replace yours in your existing ZF. I may do this or may not. Same goes for the TC. I like the 1:2. I may switch to 1:4, but don't feel swapping a perfectly good TC is worth it. Mine is original with about 90K miles, so I assume it will give up the ghost in due time and I can choose to swap to the 1:4 and maybe swap the governor in the ZF then. But it's NOT necessary to get you on the road. You of course need to take in account gearing at the diff side too. I run 4:10 with 33" tires.
It's a big project, of course. But nothing magic to it. I think the trickiest piece is going to be sorting out the electronics in a DI.
In addition, while your assuming your only spend will be on the engine and/or kit. It won't be. Once your in it, you'll find your project list grow exponentially. You'll find yourself saying: "well, since I'm in here, I might as well do this...". You've been warned.