Road Racing Duster 6.4 Hemi E85 6 speed Ms3 Pro Evo EFI

sounds like mock up tires would help.

I need some. Where do you find cheap worn out 275, 295, 315 18” tires?

Mustangs. You probably won't find them with much bigger than 275, but a lot times they'll have 255's with a higher profile that are taller anyway, and taller is the bigger issue than wider on these cars.

Go find yourself a set of Mustang Bullits with tires on them still and use those, then buy the tires you want and keep the rims.