Advice Needed - Can't Start Rebuilt 273

so you have visualy seen spark at the end of the wire? if so it is probably not spark. could the timing chain of jumped or broke? you gotta have spark, compression and fule. it sounds like there is plenty of fuel and if there is spark at the plug then that would mean its compression. could the valves be to tight and not closing all the way? i am kinda just thinking out loud. when there is a gremlin like this i think that kinda helps. you sound pretty smart with all this which i think makes it all more frustrating when you cant figure it out lol