Hi Cropper, as Roy has pointed out in other discussions , a late model AR 3 with the factory approved later cloth midrange and the appropriate crossover mod is still an AR 3 speaker but it may not sound identical the the AR 3 speaker with the phenolic tweeter. However, this is always subjective but it stands to reason that the changes could be audible to some listeners. Personally, my AR 3 speakers with the cloth mid sound very good to me but I have not directly compared them to the earlier model with the phenolic tweeter. But, they are still an AR 3 sold as an AR 3 by AR so I am not as worried about the cloth mid so much. Probably the bigger issue with reselling AR vintage speakers is whether for not they are original as replacing crossovers, refinishing cabinets , and so forth often are issues with buyers who want everything to be original. Once again, I restore my speakers with new crossover components, cabinet restorations and other changes to meet my approval and not necessarily to keep them original. I do not believe that the later cloth mid necessarily made the late production AR 3 inferior to the original as this would once again be subjective to the listener but certainly AR was not concerned as the evolution of the AR 3 to the AR3a was never considered a step back . My AR 3s do sound different compared to my AR 3a speakers but I enjoy both. I am sure you will also like the sound of your restored AR3s.
Sometimes we get concerned about issues which seem to be really important to the final sound but in reality, contribute less to the final sound than a lot of things that we have no control over since the adhesives, compliance, and other physical characteristics of these decade old drivers have changed since they were new. However, it is amazing that they still work and also still provide a lot of satisfaction to those of us that like to fool around with them.
I am sure others have their own opinions and may chime in as well, but I try to not take this hobby too seriously and just enjoy the whole vintage audio experience.
Just my 2 cents worth!