How much more would they be worth if they had say 421 woofers in them?
IMO, any difference in value would be more sentiment driven than anything else. Of course we'd really need to see those D140's. Apparently the early gray frames that twist and cause voice coil misalignment if you overtighten the mounting screws are still sought after by a few folks. The ribbed cones suggest they're later black frame versions, but as OG mentions the recone parts were all interchangeable so they could be newer cones in older frames. One can never post too many pictures when selling.

JBL no longer offers factory support/cone kits for these heritage drivers. Not unlike the 421's, their lack of serviceability has taken a bite out of their value.