"Is a Alpha Core at 12 guage air core better than the vintage Iron Core which is likely wrapped in waxed paper?"
You are definitely mixing priorities up here.. First off guaranteed that a 12 gauge copper foil will probably trounce the wax 18 gauge or whatever it is in your woofer circuit from 1970... Caps, well Caps are in a different world over how an inductor might or might not sound.. Caps are a material that can effect the signal more, an inductor of a good copper material with tight tolerance value will work well from just about any manufacturer, and in the case of the woofer I truly believe its more about how thick you can go, in otherwords a 12 gauge etc... will get you better, tighter, cleaner, and even faster low frequencies in my opinion.. Not once has a good inductor shown a problem in a woofer.. Its all about the exact right value.. By the way alpha core in connecticut I think they are still in that state will sell you a single pair of exact custom value direct if its not on the shelf with other distributors, and they do not charge any kinda premium for them.. I will admit this, the Alpha cores are not as good in my opinion on hi frequencies or midranges necessarily, but the best I have heard on woofer circuits demanding high power copper conduction, and have used them with several klipsch speakers with un-real results, but your running a vintage pro driver that barely moves I believe with tight surround, so its hard to gauge how well or not it will increase your response on that driver, but I know it will work excellent..
And by the way this "Poly Plastic" sound you are supposedly pinpointing really should not show in any woofer really, your hearing it up in the mid probably 1000 hz and higher giving you a more compressed sound, this will not occur in your woofer, your over thinking it trust me.
You are definitely mixing priorities up here.. First off guaranteed that a 12 gauge copper foil will probably trounce the wax 18 gauge or whatever it is in your woofer circuit from 1970... Caps, well Caps are in a different world over how an inductor might or might not sound.. Caps are a material that can effect the signal more, an inductor of a good copper material with tight tolerance value will work well from just about any manufacturer, and in the case of the woofer I truly believe its more about how thick you can go, in otherwords a 12 gauge etc... will get you better, tighter, cleaner, and even faster low frequencies in my opinion.. Not once has a good inductor shown a problem in a woofer.. Its all about the exact right value.. By the way alpha core in connecticut I think they are still in that state will sell you a single pair of exact custom value direct if its not on the shelf with other distributors, and they do not charge any kinda premium for them.. I will admit this, the Alpha cores are not as good in my opinion on hi frequencies or midranges necessarily, but the best I have heard on woofer circuits demanding high power copper conduction, and have used them with several klipsch speakers with un-real results, but your running a vintage pro driver that barely moves I believe with tight surround, so its hard to gauge how well or not it will increase your response on that driver, but I know it will work excellent..
And by the way this "Poly Plastic" sound you are supposedly pinpointing really should not show in any woofer really, your hearing it up in the mid probably 1000 hz and higher giving you a more compressed sound, this will not occur in your woofer, your over thinking it trust me.

