What would cause engine to jam while cranking??

Ok , can finally say I GOT IT RUNNING!!, checked the engine timing marks on the lower pulley it matched up 100% as far as TDC, got #1 up to 10 deg. before TDC, installed the dist. started with #1 , made sure firing order was correct, used die electric grease on the terminal ends of the spark plug wire, made sure I has continuity for all of the spark plug wires. HELD MY BREATH, fired up almost on the 1st crank, engine never sounded so good, ran more smoothly then ever. I am using a Mopar type dist. and ECU, resister block from Rick's Mopar, Rick Ehrenberg. Still to need clean up the wiring, take for a test drive to make sure timing is good [ no ping] need to reset carb to how god the engine is running now. Also want to change oil since there has been a lot of raw gas into the oil from so many tries to get the engine to run correctly.

Want to thank all the people here for there help, ideas, and support, have been working on this since early March of this year.
Next Sunday I have the car set up to go to a local Car Show. last year I took home a Trophy , 1st one ever,!

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