The top bushing in the distributor is good no play??

Firing order is right?

Distributor cap new and check for dizzy shaft moving up and down.

may need a dizzy collar to stop pump drive gear from jumping up and down



have another carb to try look at the step up springs with it running to see if they are bouncing up and down.

vacuum advance is on ported vacuum better yet disconnected till it's sorted out.

you sure no vacuum leaks underneath intake.

just some places to look if the timing chain is tight!