Machining is unavoidable in your case, unfortunately.
The AP Star 12 is from 1991.
In 2011 I was able to upgrade it to the current AP 2-speed focuser easily by simply threading on. It’s a good system for easily changing focusers, a system still in place. Although in 2011 the focuser was half the price of current ones.
Yeah, that's a gorgeous scope! Since I'm moving to M117 threads, it will be fairly upgradable in the future since it'll be a standardized thread size that are used by a lot of different focusers. I consider an Astro-Physics scope to be a "modern" scope, so upgrading parts that adds to extra utility and performance shouldn't detract from its value and desirability (in my opinion).