Double check the plug wires and confirm that you have them in the correct firing order. I just had a friend of mine who was trying to get a newly rebuilt 283 running right. Was running rich, stumbling, cutting out, restarting. He swore up and down that he had the wires right. He ended up taking it to a mechanic who discovered . . . He had a plug wire crossed.
If the wires and carb are right, could be the mechanical advance. Easy to check as noted above.
The photo with the distributor body shows the cap, spring and Bakelite bushing arrangement. Finding some nos Bakelite spacers is near impossible, at least for me anyhow. I use delrin as a replacement. Best is to get a rod of delrin and have someone with a lathe cut it down and then cut you a few pieces, about 1/4. You can find delrin rods on eBay. No access to a lathe, chuck about 1 inch of the rod in a drill press and spin the rod, use a flat file to shape the diameter down, then cut 1/4 piece.
The photo with the grungy advance mechanism was a distributor I just recently rebuilt. I had it on the sun machine and it would not advance at all. Once I took it apart I discovered why. If you look closely, you will see that the spring for one of the two advance weights broke off its pin and jammed in between the advance weight and the plate. So no advance. Might be your problem also, or it could be a lot of rust or crud gumming the advance up. You might not have anything wrong but it is another place to check for a problem.
The next photo is an advance with the retaining plate installed, and one with the plate removed so you know what you are looking at when you take yours apart.
