The test with the spark plugs removed is important, because jump starting with 12 volts can hide a tight rotating assembly. If the pistons and/or bearings are too tight you really don't want to make the problem worse by forcing the engine to turn with high starter torque.
We're swimming upstream at this point because apparently some preliminary steps like pre-soaking the cylinders with lightweight oil or Diesel fuel, etc. apparently was not done prior to trying to start the engine. I usually spend a week or more checking the basic mechanical condition of an engine before I make any attempt to start it. That includes lots of pre-oiling, soaking the cylinders and valve guides with something like PB Blaster or KROIL, compression testing, spinning the engine at no load with the spark plugs removed, etc. Actually making the engine fire and run on its own is the dessert course of a meal- - - - -not the appetizer!
Jerry
