The Ebay seller has added clear pics of the S/Ns and cone numbers.

Altec 604 Dual Concentric Speakers with Mantaray Horns. Rare vintage duplex spks | eBay

Some more info. The Altec/Mark lV Repair PartsLlist(March 1, 1996) lists the recone kit #R904/604-8HP for the 604-168X, 604-HPLN and 904-8A LF speakers. This kit has a LF cone described as HI POWER. Unfortunately I have no information re the cone part number for this kit. Other model LF drivers are listed as having a HI POWER cone. Altec may have used one of those cones or come up with one for the 604-168X, specifically. Another Altec mystery, maybe.