Advice Needed - Can't Start Rebuilt 273
Are you sure you are firing on the compression stroke?
X2........How did you set the timing, exactly?
1----Even if you are absolutely ABsoLUTEly positive that you correctly installed the cam and distributor, things are possible.................
2-----You might have gotten a reverse rotation marine cam
3-----You might have a misground (rare) or mismarked cam drive, so check the cam timing independently of timing marks. You do this by checking at what rotational crank degrees the intake/ exhaust events occur. Even if you don't have a degree wheel/ timing tape or a degreed balancer, you can calculate degrees per inch around the balancer perimeter.
4-----Either by mismatched parts or "slipping" of the balancer, the timing marks may not be correct, so verify them with a piston stop
The FIRST thing I'd do is use a piston stop to be sure the timing marks are accurate, then go completely through distributor setup to be sure it is actually timed correctly.
http://www.forabodiesonly.com/mopar/showthread.php?p=1969786849