Since the RT4 is so new I've not read any posts covering those two subjects.
It appears Back Draft has stopped selling their track based cars as well.
I'm honestly surprised you got a response (someone answered the phone) at the Boynton Beach Backdraft shop.
The FB site Back Draft Owners Group is primarily focused on Tire stickers, and how can I get noticed issues.
Best bet is to reach out to Jay (aka Cashburn on this site) @
https://vintage-motorsports.com/ as they are always on the leading edge of BDR mods.
Also try Radical Roadsters in Tomball TX. James Yale is great to deal with .