what tire size for 10 holes with 3:73's?

If you're just planning on running them out back, a 265/50 is the absolute wides I'd go on a set of ten holes. You'll probably need to flip your quad shocks to use them and even then you might get some rubbing. I've got a set of 255/60/15 drag radials on a set of 15x7 V6 Mustang wheels and the bulge quite a bit. Don't bother going any wider than the stock 225's out front unless you're going to shorten the side walls some (IE, with a larger wheel). All big tires, with a tall side wall do on a narrow rim when they're in the front end is make it dart back and forth on the road. Your handling won't improve any and may actually get worse with so much side wall flex.