All I can say is I used a 77 or 78 9 1/4 out of a full sized truck under the rear of my 39 pickup that sat on a 91 Dakota frame. It was fender less with 8" wide steel slots off a 70s Dodge truck. With the Dakota 8 1/4" rear the tires did not claret the bed sides.. (pic with the full sized rear end).

The Dakota 9 1/4 were all 6 lug wheels, so as far as I know, the only 5 lug axles for a Dakota 9 1/4 would have been in the mid 2006 or 7 vintage, and those had a different bolt pattern then the 5 bolt full sized trucks were. Early Dakota trucks (88-96) had a 4" narrower wheel track then a full size truck of the same model years. The 97 and newer Dakota trucks got a wider wheel track, but that may have only been because of the wheels that were used. The las edition of Dakotas got 5 lug wheels with a different wheel bolt pattern, who knows where Dodge came up with that bolt pattern, or why.

By "offset" I am assuming the OP is concerned about the position of the pinion shaft for comparisons to the length of the left side axle and the length of the right side axle.