I never use run in (break in) fuel. I always break in the engine with what I run at the track. O'Donnell 30% with 12% oils. Just be careful and watch your temps. Don't run to rich at first and make sure you spin flywheel after running to bottom dead center to pull piston out of pinch area of sleeve.

As far as diff oil is concerned, I changed to 3f 7c 1r. We have a lot of tight sections on our track and I wanted as much steering into the turn as I could get. I do agree that it is anybodys guess what is the best set up but I may try a thicker center weight, maybe 10k in the future to apply more even power on both ends. I like the lighter weight in the back which I beleive helps with steering.
Who knows the right answer. I would walk around on race day and ask the fastest drivers.
Rockman