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?
i wouldn't spend a thin dime on what's cooking there.

motor & trans swap time.

find a full pull, slam it in there. poke a hole in the floor and run a universal shifter and roll.

on a rebuild the work isn't difficult, the parts aren't crazy expensive or very difficult to source. but the machine work for the block, crank and likely head will eat you alive.

unless you have a 5 gallon bucket full of $100 bills, look for a viable motor and trans to make the swap.