If I remember correctly (big IF) '84 D100/150 rotors have the larger outer bearing needed for the Dakota spindles but maintain the 5x4.5 bolt pattern.

Perhaps somebody with more free time and a better understanding of suspension geometry than I have (Ackerman, bump steer, scrub etc) could get their hands on a set of the drop spindles for the A/B/C/E/F/J/M/R bodies and see if there is any workaround to using those. Even if a custom lower ball joint/steering arm had to be fabbed it might be a better alternative to what is currently available for the D series trucks.