I ran my Duster with a 318/904 and 225/60/15's for awhile when it still had the 7 1/4 in it. Heck I even managed over 500 miles on it when it was behind my 400+ hp 340 with a 4 speed and 225/60/15's. No launches or burnouts with that set up, and it was still working when I finally got around to swapping it for a 8 3/4.
With a /6 and those tires you should be fine as long as the 7 1/4 is in good working condition. If it's an auto trans you really shouldn't have any issues.