Talk about obstructed exhaust, I got it to run a bit, and you should of seen the mice nests come shooting out!

I loosened the distrib clamp screw and turned the distrib back and forth to loosen it up. I rechecked the timing mark and rotor, set up the points, and replaced the plug wires in proper order (1-5-3-6-2-4). I pulled out the choke, pulled the throttle out quite a way, and turned her over. It popped once, it popped twice, I pushed the choke in, it fired and turned, fired more (with a few backfires), and then took off to the races at high rev! I throttled down and let her run for a couple of minutes. As I eased off the throttle more the engine lost power and quit. I have started a few more times the same way. I am concerned about the backfires, and why the engine "overrides" them when it gets going. Probably need to tune-up some more.

1953 GMC half-ton