Simon,
Blow-by is very normal for any fresh engine, the rings need to seat and the "break it" period needs to pass.
If you have a higher lift cam, the amount of vacume you are pulling may not be enough to remove all of the gases from the crankcase ( at the beginning ).
If it is spitting
oil out the cover holes, i'd worry. Run the engine for 500 miles and check the blow-by again, it should be almost non-existant.
Keep in mind, this works off vacume. If you put your foot in the carb, you have NO vacume to speak of.
Actually, I am going through the exact same process right now and after three hours, the smoke is much less.
Just my $0.02
