when it's tunning rough that could as well mean that it's running rich.
Dwell angle too small means the coil has less time to charge. Points need to be adjusted every now and again (they burn down) or replaced. Since you have a dwell meter consider yourselves luck and just quicky adjust the dwell. that 2 mins work.
Yes, check as well on the distributor shaft. If that has play then I would replace the distri.
For running rough check as well the vacuum advance. put some vacuum (worst case with you mouth and hose) on the vacuum canister and see if it can hold it (i;m quite sure it does as you mention that your idle changed _a lot_ when you connected to manifold vacuum).

I'd say everyone here on the forums will recommend electronic ignition.
I personally went for Pertronix flamethrower II distributor and coil for the following reasons.
looks similar to original as coil is still seperate from distri, you have a new distributor (my orig was rubbish) and high performance coil for reasonable price, but some people had hassle with them
some will recommend those big massive GM distries. They're great as the parts are available in every parts store, but it will never fit with original or round 14" aircleaner. I've seen 2 mustangs already driving without aircleaner since they put in that thing (they're waiting for new smaller aircleaner to arrive).
and then there are MSDs. They are as pricey as they are great, but I don't recommend them when you use factory tach or rally pac. loadsa problems (destroyed tachs or doesn't work)
All the others I can't comment on

 

now that you mention it. Ya. fully agreed :-)

 

Set your dwell and then get a timing light. Adjusting timing by sound is just plain dumb. Pinging under load is too much timing which will put a nice little hole in your pistons or worse.....too little and you will have all kinds of drivability problems. Bottom line: get a timing light.

 

Once you get the timing light and dwell right, ask how adjust the idle.
Get a vacuum gauge while you are at it.