if your heads are good and the inspection proved no mechanical defects than throw a set of lifters at it and put it back together and see what happens. when you did the coil swap your "assuming" the electrical harness connector for that cyl 8 is good, i would make sure it's good. the cyl was absolutely "cold" either from a lack of compression or ignition. run that piston down an inch or two in the cyl and pour a couple ounces of oil on the piston and see if it leaks past the compression rings, if it dosent that is a good sign but does not rule out a broken oil control/scraper ring. i think you would have some marring in the cyl if a ring were bad? the lifters are a shot in the dark, i think with that many miles the cam should be replaced if new lifters were to be installed, factually your efforts have proven cyl 8 missfire but no cause, keep it cheap with "guess parts". simply replace the lifters for that cyl only? put it back together if the fluid leakby test is acceptable, start it and if it still misses leave the plug in the cyl and slave another into the plug wire and ground it, start it and confirm good spark. i know PITA, but the alternative is take it to a shop and spend thousands. also im just "shooting from the hip" consider everyones opinion and hopefully you will "get er done"