Can you define this blowby?
Some is normal, excessive is not. Excessive would be like a freight train under full load coming out the breathers, normal would be like a lit cigarette inside the valve cover.
Keep in mind it needs time to seat the rings, I've seen some real smokers that calmed right down once it was broken in after 1000 miles...usually because of a coarse ring hone etc.
Sounds like you haven't even broken the engine in yet, relax and give it time. In a good thousand miles is when you need to worry about it...if the plugs look OK it might just require patience.
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”
— Han Solo