Welcome to CHR!

I see I'm a bit late to this party but what I read is rings not seated - 20% leak down means when you're engine is running you are really pressurizing the crankcase. the puffs you see out of the breather are, in all likelihood, atomized oil. If the cylinders were properly honed, the the rings should seat within the first 25-30 miles. If you've gone 100 miles, there is little chance they will seat beyond where they are right now. Do you know if the bores were honed to a 45 degree cross hatch after the bore?