Back in the day---pre-internet and penny pinching days, I remember not being able to find a Duraspark adjustable advance. They all had like 20 or more degrees, for use with EGR. But, the one for points distributor was available and adjustable to get the range I wanted. Now days we can search to find something made to fit instead of modifying a different part.
Yes, I was using the big cap, I marked on the cap adaptor where each wire post is, left the cap off. Then hooked the timing light to the coil wire to see where the rotor phasing was and where it flashed over each post and it didn't look bad. It didn't seem any further out than what the vacuum advance normally does to phase. Perhaps if I were pulling over 20 degrees it may have gone too far, but I think at the time I was trying to achieve 8-10 in the vacuum.
Maybe I will try a Crane advance next time.