Little Ben, you been hanging around Roy from PA?
I agree thats a lot of weight to loose. I'd personally attack it from two angles. I'd first sand the limb edges through the taper out mid limb narrowing the limbs. Then I'd flat sand the fiberglass. Most bows loose a lb for every thousandths. Depending on the thickness of glass you used you'd need to drop 5 th off each side just flat sanding but edge sanding should drop it a few lbs right off the bat.
From my experience it seems like you sand and sand and very little happens then it happens quick! Take your time and keep a eye on tiller.
Then theres always Little Bens suggestion! lol