Max tyre size different on ss springs?

Not without either doing the 68' Hemi car quarter cuts or a mini tub and spring relocation. A 255 will squeeze in there with the right offset rim and a inner fender roll. I run a 245 in the rear but I have a rear sway bar to stop some rub'n. I won't mention the hill billy air shocks to jack the *** up enough to get them to clear.

I have a 69 Dart. 67-up Barracudas, Dusters, and Dart Sports have way more room due to the open quarter skins vs the Darts truncated skin.