The 87-90 Dakotas used a 5 on 4.5 pattern. 91-04 use 6 on 4.5. 05+ are 5 on 5 I believe...
The 8.25 found in in any 96 and older Dakota will have 27 splines, so it is weaker in spline count and gear size than even a ranger 8.8. The 9.25 found in most 97+ Dakotas are 31 spline and are decently strong and you can probably get custom shafts but really, you're a lot better off just doing a 31 spline 8.8 swap.