[dontlifttoshift]

What if I told you that a 315/30-18 and a 305/30-19 have the same sidewall height?

You have 14.5" You need .75" to the inside and .25" on the outside assuming you are running some type of link suspension. Those are your minimum clearance numbers. You can run the outside tight as most 67/68 camaros don't travel enough to actually tuck into the fender much anyways.

So your maximum section width is 13.5"

325/30-19 is 13" wide on a 11.5.....put it on a 12 and you get 13.25"ish.