After reading all this Ill chime in, Sounds to me like you have your timing chain screwed up, thats whats causing it to pop through the carb, I have been through all of this with numerous times,it ended up being my timing chain once. I doubt its your timing, if you have been moving it and tried it everywhere then i think it would have fired. Are you flooding this thing? thats something else you should look into. Yes two piece timing covers are the best, makes cam changes easy and makes checking your timing chain really easy, your most likely gonna have to pull this motor back apart, drop the pan and pull the timing chain cover off, make sure your marks are aligned although i run mine at 12 and 12 instead of 12 and 6. Bad news is i hope you havent been cranking all day like you said, if so i dont know how well that cams gonna hold up, thats an easy way to destroy one. If you have spark, and your valves are adjusted right then im gonna go with timing chain. what kind of cam is that? solid? hydraulic? roller? how are you setting your valves? I use the cap, when the rotor comes around and points at the number one plug wire(point on the cap) then adjust number one intake and exhaust, then turn your crank to the next wire( or point on cap) and adjust that cylinder (8) then 4-3-6-5-7-2 etc. Well keep everyone posted on your progress. good luck