Mini Tube on a 71 Camaro

[SPEEDSTREAM69]

Hello,

Looking for some help, I would love to fit a 335/ 18 on the rear of My 71 camaro
but not sure how big of a project that will be.
Has anyone gone through the process the can spare some advice.
If this is to big a task I will have to go down to a 295/18 (should fit without any massaging)

Thanks