Engine of barn find-steps to evaluate/save

Well shoooot... I tried the "hose in the cylinder" test. The front 5 seem to show up and down movement, BUT that last cylinder, in the back, seems to be staying in the same place. The hose, on cylinder rotation, jiggles a little, but that could be a valve moving it. How difficult is a rebuild on these? For all I know the auto trans could be trashed as well.. Body has plenty of rust to fix. At what point is it just not worth dumping money into?
Folks practically give Slantys away stock, the problem is the proximity of the parties usually, & the timing. It's worth throwing a pick-up stock mill in for what they go for, to make it a runner, the only thing to watch for is any '68&^ crank needs a spacer ring to center the smaller '67& down torque converter's smaller hub nose. They pop up here all the time, & FB-MP, from free to $$$ depending. Look back through the Mechanical Parts for Sale forum, & use the search function there as well.
P.S. That engine would've had a road-draft tube, not a PCV system originally in that car, so either the engine or the valve cover & related PCV components were changed out.