Bmdduck,
I would try rebuilding the crossovers before replacing speaker drivers. The crossover designs on the old Snells was very good, but (like most speakers of the era) was limited by design in order to hit a manufacturing price point. Also, time is not friendly to old capacitors. Rebuild the crossovers (or get someone to do it for you) and I think that you will hear more transparency.
I would try rebuilding the crossovers before replacing speaker drivers. The crossover designs on the old Snells was very good, but (like most speakers of the era) was limited by design in order to hit a manufacturing price point. Also, time is not friendly to old capacitors. Rebuild the crossovers (or get someone to do it for you) and I think that you will hear more transparency.