I own a 3600 and as a rule I would say the 3100's sell for more because they are smaller (fit in the average garage), are easier to find some parts for, and tend to be more available as a rule in many different conditions. You see a great deal of them hot rodded, a like number completely restored and a significant number of project trucks in between. It is a matter of choice, I like my 3600 and bought it to restore. The idea of swapping components is problematic, everything on the frame is different on both trucks. You would be better off to pick one or the other. As to your truck being a 3100 vs. 3600 run the data plate number through the Vin Buster in the Tech Tips section. My guess is if you have 8-lug wheels you have a 3600 truck.
