68 Val, time for new tires and maybe wheels.....

Forget 15s, the tires are hockey pucks. 17s are problematic on later model disc brake setups with tie rod interference issues, depending on wheel choice (many go with mustang rims). 18" wheels/tires offer the most choices for fitment but are, as they say, not everyone's "cup of tea".
I roll on 255/40x18 back and 245/40x18 front on my '67 and love em