Looking at some specs I found, the dual piston calipers for the 2500/3500 and 1500 4x4 on the '00-'01 have piston sizes of 56mm and 54mm respectively. The older single pistons are of greater difference. The 1500 has 75mm, 2500 2wd 80mm and the 4wd 2500 and all 3500 have 86mm pistons. The rear wheel cylinders vary depending on year. '94-99 1500 and '94-96 2500 have cylinders with a bore of 0.937in. 94-99 3500 have 1.06 bores. All 00-01 trucks use cylinders with a bore of 1 inch.

Personally I wonder if it's worth it to go 94-99 3500 wheel cylinders and the 00 2500 calipers on my 00 1500 4x4?

 

As I understand it, the dual piston caliper is a different mount.
1500 and 2500HD/3500 are different mounts.
The single piston 1500 and 2500LD are the same casting/mount with larger bores... these are directly interchangeable...