Don't know the answer as to whether the trany from the 2500 will bolt up or not, but seems to me if its from the same motor it should.
As for the conversion, get read for a ton of fabrication. Things that come to mind are:
1. Trany mounts.
2. Removing the automatic shifter.
3. Clutch master and slave cylinder install. Yup, its hydraulic or at least they used to be.
4. Clutch pedal install.
5. New drive shaft. Manual tranys are usually shorter than automatics.
6. Most likely will have to do some work with the computers in the truck to teach it the auto is gone and the manual now exists.
Those are just the ones I can think of. Others will be along to either add more or tell me I'm full of it, which has been known to happen in the past.