Here's a chart and a calculator that should help converting the ratio to ounces per gallon.

http://www.rctek.com/pdf/fuel_to_oil_ratio_chart.pdf
http://www.csgnetwork.com/oilfuelcalc.html

Thanks!

Maybe I am mistaken and 32:1 is the recommended fuel mix for my Lawn-Boy #5247 and #10550. I had heard that you could use less Mobil 2T Racing Oil, than what is recommended.

All Lawnboy 2 cycles, except the M series, call for 32:1 mix ratio. It is always a good idea to follow the manufacturer's recommendation on oil mix. That said, modern high tech oils are much better and I don't believe that a higher ratio will hurt but I don't go over 40:1 in anything I run and that includes my new Stihl chainsaw that says 50:1. Many professional woodcutters run a little thicker ratio, saying that it runs cooler and gives a better ring seal, thus more power. I have been running Mobil 2T in my L21ZPN at 32:1 for over a year now with no excessive smoke or carbon build up. I just like the safety factor of a little more oil.

Let me rephrase that. All the models as new as you listed call for 32:1 ratio. The 3 ring D400 and older models called for ratios of 16:1.

I would follow the manufacurers specification for mix ratio unless Toro(Lawnboy) indicates that the newer oils can be used at a higher ratio.