Got a pair of JBL 4310s from eBay a couple of years ago. They were in poor condition when arrived. A cabinet was cracked during shipping. The grey surfaces were painted in black ugly. One 2212 had rubbed coil and I finally had to replace it with a spare 123A-1. Despite the poor condition, they sound quite nice to my ears. Compared to my bass shy Klipsch Heresy, these 4310s can render more details and of course have better bass.
When driven with my DIY KT66 PP amplifier, the combo can handle rock music much better than the KT66 with Heresies. I can finally feel the energies of Red Hot Chili Peppers, Pink Floyd, Jamiroquai, Jimi Hendrix, and even Metallica from the combo. Although far from satisfactory, these 4310s seem to have more potential than the Heresies.