Mark, a couple things to think about.
1) MSD basically copied the duraspark distributor to come up with their design.
2) The duraspark distributors were first released when small caps were the norm. This means you can install a small cap for the correct appearance if you desire, just be sure to get the accompanying rotor that goes with the small cap.
3) If you will alter the advance plate slot it is 0.026" per each 2 degrees of advance. (.013" per degree). This means you measure the slot as is, then weld and file to the desired advance limit slot dimension based on your measured needs.
4) Adding bushings to the slot limiter post is another way to modify advance plate movement. If you have the plate out for work it is a good idea to modify the post to be highly consistent in measurements, this way you can then make any desired limiter bushing to drop over the post...They are stamped from the factory and not terribly accurate from a machined part perspective, but they work just fine as-is so you don't NEED to true them up.
5) Bending the advance spring mounting post (tighter for later/higher rpm limit) will be that final adjustment to get things exactly where you want them, but it is a great place to start if your advance limits are close already....and easy too because you don't have to take things apart much to get at them.
Good luck. Timing events may be one of the most commonly misadjusted portion of an engine as well as the couse of many problems that seem to be coming from someplace else.
Whenever I get asked to help tune a carb I always start my process by verifying the timing events and getting that squared away first....the rest of the tuning depends on that being correct.
