Hi,

The 3W-70 twin weighs 4.95 lbs and is only slightly more than the 3w-50 or the 3W-75 iUS. Perhaps Tom has this older engine confused with the newer 70 rear carb singles which weigh a lot, or the newer 78 twin which is a heavy engine.

I have the same engine as you on a 33% pitts and it balanced fine. The plane flies like a rocket with unlimited vertical

Hope this helps

Elson