I have to say that back when Halcro asked about setting up his cartridges in separate headshells so that each cartridge could be used with each of his tonearms (at the time, I thought he wanted flexibility among several tonearms, not just 64S and 66S), I was dubious that this could be done without at least some minor re-alignment each time. (And we know there is no such thing as "minor" realignment; each time one must do it, it is a pain in the arse.) Later, when Halcro claimed he had conquered the problem, and since he was pleased with the results, I assumed that perhaps I had been wrong and /or that Halcro may have found some compromise that is "good enough". Now that the issue appears to have been put before us again, I am interested.
Right now, the question seems to be that if you mount the 64S at 230mm and the 66S at 295mm (factory recommended, as I understand it), then a headshell bearing a cartridge that is correctly aligned for use on the 64S will also give perfect alignment when that headshell/cartridge is transferred to the 66S. It would seem that someone who has actually done this using a quality protractor to evaluate alignment on both tonearms could tell us the answer. Also, Euclid could tell us, if he knew the other relevant parameters.
Right now, the question seems to be that if you mount the 64S at 230mm and the 66S at 295mm (factory recommended, as I understand it), then a headshell bearing a cartridge that is correctly aligned for use on the 64S will also give perfect alignment when that headshell/cartridge is transferred to the 66S. It would seem that someone who has actually done this using a quality protractor to evaluate alignment on both tonearms could tell us the answer. Also, Euclid could tell us, if he knew the other relevant parameters.