Frank, did/do your Advents look like the picture in this thread, other than the woofers being all-metal ones - no Masonite? In other words, are they original Advents and not New Advents?
I ask because, if you bought them in 1978 and they are original Advents and have all metal woofers, that reinforces the theory that Advent used the all-metal woofers on the very late original Advents, since 1977-78 is when they started selling the new Advents.
Original Advents have tweeters like those in the picture, whereas New Advents have tweeters that have no Masonite square and mount flush to the speaker board (baffle).
Doug