For swapping a diesel into a gas car, the diesel parts donor vehicle does need to be a manual trans car if you want the finished result to end up with a manual. The gas recipient body does not need to start out as a manual car, but it makes the conversion somewhat simpler if it does (otherwise there is some extra effort to convert from auto to manual, as well as gas to diesel). The extra work is not complex, and the manual diesel 200 series donor used as an engine conversion parts source whould provide all the parts for the manual conversion also, but it does add a few more steps on top of what is already a considerable rework of the car.
On the other hand, though, the most important aspect is to have the end result as you want it. If you were to build a swap car starting with a gas body and you found a recipient candidate that ticks all your other boxes, I wouldn't let an auto>manual swap dissuade you from going with it, versus finding a recipient that does have a manual but misses other goals (i.e. worse cosmetic condition, color/year you don't like, etc). It's just one factor among many, not a deciding factor.
Put differently, converting an otherwise ideal automatic car to manual shift might very well actually end up being less work than having to do bodywork restoration, interior restoration, etc on a car that already is set up for manual transmission but needs more help in other areas. It depends on the individual vehicle.
I'll send you an email with some info on a diesel 260 wagon I know of that is for sale a couple hours west of here, in case it helps.
