Bill:
I am back into the game after many a moon away as well.  But I do run Fox 35's on my Flight Streak and Ringmaster. Break in is pretty straight forward. I use the Fox fuel 5% w/29% oil and 10/6 prop.  On the bench, run a tank (3 oz) at slightly rich(kind of a 4 cycle rumble, Fox 35's do shake and rattle a bit.) Then I run another tank just get it into the 2 cycle mode.
Then I take it out and fly. I use the Fox 5/29 for flight also.
Since the Fox 35 does vibrate a bit, always good to check engine mounting bolts before and after every flight.
I am sure there are plenty of fellows on line that would have more detailed and supportive information. Maybe they will jump in here.
Hope this helps.
Jim

Walter has it right. PowerMAster GMA 5-29 All-Castor is just as good as Fox Superfuel. Don't skimp on the Castor! Do use a 9-4 prop, and wood, if you really like your fingers as they are; APCs are guillotines!

It's not really a matter of how much bench time, but the quality of that bench time. I remember folks saying they'd hook up a quart of fuel to a Fox .35, start it and go do something else for an hour. That doesn't work! What you need is repeated "heat cycling". You'll accomplish more in 30 minutes of 2-minute runs with a full cool-down after each (say another 3 minutes) than you will with the aforementioned quart of fuel and an hour.

You'll be able to tell the engine is ready to put in a plane by the way it "breaks". Most of the break-in should be a series of 2-minute runs at a fast 4-cycle; blubbery rich only pounds out the main bearing. As you near the 2-minute mark, pinch off (and hold) the fuel line to kill the engine; this will give you a 10-second burst of lean running.

After about 5 of these runs, when the engine is warmed up, pinch the fuel line for 1 second. The engine should break into a 2-cycle for 5 - 15 seconds and then drop back into a 4-cycle. IF it tends to stay in the 2-cycle mode, it's not ready. When it reliably breaks lean and then settles back to a 4-stroke run, it's ready to fly, but don't chance a lean run for at least another hour of flying.

FWIW, Larry Foster recommends 10% (minimun) Nitro in his engines. More power at a cooler operating temperature.

Using the hard rubber 1/4" dia. Dremel bit, running round the inside edges of all the ports, and the top and bottom edges of the piston, works wonders in eliminating all those little scratchy burrs that give the traditional tramline scratches up the side of the piston.  Combined with the other advice in this topic, will lead to a good long life.