Steve Weiner at
Rennsport Systems does this conversion using the trigger from a SC donor. I don't know what he used for advance, but IIRC mine has about 16° of mechanical advance.
On his conversions, you set the timing by rotating the trigger inside the distributor. It is more of a hassle than simply rotating the dizzy body, but once you set it you don't really need to mess with it again.
Honestly, even if you did make a timing slot around the mounting stud (which BTW needs to be longer than stock), there isn't much room to rotate the distributor body to set the timing. It is pretty tight.
Tom