I may have found what I am looking for. I looked at a 79 D50 Sport that has been sitting apart for the past 13 or so years not far from me. It has the 2.6l engine and the owner has a head that is not cracked (visual inspection only). The truck is in a sorry state, being taken apart and out in the elements for a very long time. However, it has a good amount of usable parts - most importantly the head and valve cover. We are negotiating on price, so I may end up with an entire parts pickup.

This may solve my engine issues and could potentially get my D50 back on the road sooner.