Rick,
I've gotten wheel inserts in the past from Prestige Wheel Accessories www.prestigewheel.com
They've got several different sizes and types. I'm not sure if any of them match what you're looking for.
I can't speak for Jeff, but I think he's looking for more adjustability rather than necessarily more stiffness.
The TR8 has a goofy front suspension design. It's a strut type suspension, but instead of a lower A-arm, it's got a lower I-arm. Then it uses the front sway bar to sorta-kinda act...
I’ve got a new 15” Kirkey intermediate that was an inch too narrow for me. If it’s something you are interested in, I can dig it out and verify the model number.