That allison setup sounds pretty cool. Is there something wrong with it? 4x4 versions of the d-series pickalls use the NP205 regardless of what transmission is up front, so you're good there. If you weren't opposed to going with manual trans, you could swap all the necessary parts over from your 2wd donor and be good to go. The t-19 will mate up to the divorced t-case. With what little I know about your situation, this May well be your best option. To stay auto, you'd need all the associated parts from any d-series ('69-'73). The '74-'75 rigs have set back engines and the auto shift linkage on those is total crapball garbage to be avoided like the plague. Also, the autos in early d-series, at least through '71 were borg warner models, which aren't bad units. They just aren't as popular, and therefore support in the way of rebuild kits and torque converters isn't nearly as good as it is for the 727. '72 was a transition year for autos in IH rigs, with the remaining bw inventory being phased out in favor of the 727.