Discussions about the L65 and the 4425 and other speakers have often centered around need for a 12" JBL woofer. I would suggest people consider the 252G. It is a modern woofer with neodymium magnets, differential drive, dual voice coils with a third braking coil to dampen excursion overrun, and a no-rot rubber surround (yes!), etc. We JBL nostalgists need only overcome our attachment to 12" drivers with 4" voice coils.
I have been listening to this woofer in the LSR32 for several months and think it is quite impressive. I have not found a data sheet on it, but you can find some description of it in the panels on the LSR32. In that speaker the 252 is crossed over to the midrange at 250 Hz; so I have a question about what it's upper limit should be. As a twelve inch woofer you would not want to try to use it much above 1000 Hz anyway.
I know that also George Augspurger has used this woofer in custom monitors. In more than one he used it with the TAD 4002. I don't know what crossover frequency Mr. Augspurger used, but Pioneer gives the 4002 a minimum specified crossover of 600 Hz. Mr. Augspurger included an 18" subwoofer in this monitor system, so I would think that would free the 12" to be used at least up into the high hundreds.
Giskard ran the numbers on this woofer once and it looks to be a suitable replacement for the much mourned 2203 in a cabinet of about 2.5 cu. ft. It's in this thread discussing the LSR 32.
I think the 252G would likely be an improvement over the stock woofer in the L65, although crossover modification would be required. Note that the L65 cabinet is probably just under 2 cu. ft. net, so Giskard's plots would not apply directly to that use. In the smaller LSR 32 cabinet it is down 3 dB at 53 Hz in a half space. It has a 28 Hz tuning, which I think gives it a roll off with little knee, a tuning that works well playing to room rise, especially in a smaller room, which, after all, is the kind of space a small monitor is designed for. In a larger space, like my listening room, you would want to plan on a larger cabinet or the addition of a subwoofer.
Retail price on the July 1, 2004 list is $233 and change.