Am I correct to assume it's a M1028 because of the dual wheels.......
Not necessarily. The military didn't buy any dual rear wheel CUCVs from the factory, all were later conversions from a GM kit provided in a big crate and were usually converted at depot level, but many were done at unit level.
M1028 and M1028A1 were both single rear wheel trucks. M1028A2 and A3 were dual rear wheel trucks.
M1028A2 were converted from M1028A1 and M1031, which had the NP205 transfer case. M1028A3 were converted from M1028, which had the NP208 transfer case.
As an example, my M1028A2 started life as an M1031, and has both its original data plate and the depot conversion data plate on the door frame.
All that as clear as mud?
The attached charts from the CUCV manual helps with which trucks came with what stuff.
Cheers