NV4500 swap.

Only thing I've seen in 1/2 tons is the 3500
They also got the NV2500 and AX15 in some years- I've always thought those were Dakota-only, but I found a 2500 in one half ton and pulled a spare AX15 for my Dakota out of another... it seems like in some years they used whatever they could get the cheapest or was the most available (that almost sounds vaguely AMCish, doesn't it?).