A stuck flat six doesn't have much value unless it can be unstuck relatively easy. They are expensive to rebuild. The most valuable part is the exhuast manifold as long as it's in good shape with the mounting flange and bolts still in tact. These manifolds tend to crack in this area.
There might be some value in the tranny but it sounds like with the PTO it's the heavy 3 speed which I don't think is as valuable as the light duty 3 speed. If it is the heavy duty 3 speed I think it should have the hoghead, the casting between the transmission and the flywheel bellhousing. This part is used by hot rodders to install a modern transmission behind a flatty.
Most of the panels I have found in my area, not many, but a few were owned by farmers who used them to haul eggs to market. Maybe they were also used to run pumps or other farm implement. I don't know for sure but that's my guess and I'm sticking to it. Farmer can be very inventive with the use of their equipment, remember, I live among them.