Old 15x6 Cragars, Tire Size?

Yeah, my Indy 500s are brand new, still have the nubs on them, but decades old and the treads are full of cracks.

I checked tire rack, helpful, but I was surprised that with tax, free shipping, and the best local shop to install that had a reasonable price, I'm looking at about a $24 savings.
I happen to have a $40 coupon to the local place as well, so it's a wash.

Still, I thought tire rack was a deal, but everytime I look at specific tires it's barely worth it.