Stiffer springs to prevent rubbing

So my 68 is running 15x7 w/ 225/60R15 front and 15x8 w/ 245/60R15 in the rear. I have occasional rubbing I’d like to do away with before it ruins my tires and wheel lip trim. Both the front and rear rub occasionally, the rear more so when the car is weighed down with passengers and stuff in the trunk. All the suspension on the car is new, so it’s not a matter of sagging springs.

I know the easiest solution is to run a narrower wheel/tire combo (I knew a 245 would be pushing it on the rear when I got them), but the budget doesn’t quite allow for that at the moment.

Do you think running stiffer springs would solve the problem, or don’t waste my time and just save up for narrower tires?

Do you have room to change the rim offset?

Plenty of room to tuck in more, especially in the rear. But I don’t think those styled steel wheels are available in different backspacing unfortunately.

I know there are several wheel shops out there that would remove the rivets, weld the holes, and re-rivet the rims. I had a set of original Kelsey Hays magstars redone by a place in Colorado several years ago.