robk - Lonnergan ran a modified 12L last season. It used a thick chassis plate (they made a small run of these), dampening tubes and the "old skool" front suspension. He used the upper pod plate from the oval car to make this conversion. Blackstock ran the disc dampening system, but a 12LC chassis. Henderson ran the same as Lonnergan. I don't see a new 12th scale from Associated in the near future. [now maybe having said that, they will do it]
The best way to make a conversion to dampening system by tubes and rods is to use either the CRC conversion or the IRS conversion. The IRS conversion also gives you a thick chassis that is well suited for carpet. It is a little stiff for pavement. Word has it that Paved Onroad Nats 1/12 Stock Champion Mike Dunnigan wanted to cut some bracing out of the IRS chassis to get more flex for the conditions. I don't know if he actually did it, but that should be in your consideration for selecting a car to run. I wish Stormperson would have run better at the Nats so we could brag about his Speedmerchant REV3. One chassis seems to fit both carpet and pavement.