"Minimum" blowby measured how? By sight or using a manometer? My advice, have the engine evaluated by a reputable engine shop before spending $25-30K on a rebuild. Even if there is excessive blowby, you're going to want an inspection of your rods and mains in order to determine whether you only rebuild the top end or go the full Magilla and include the bottom end as well.
My bad...reread and saw head gaskets NOT valve gaskets. I'd still have both bottom and top ends evaluated.