I have a set of stock 76 cc heads. I was wondering if I could have them milled to get a 64 cc, and if it is possible how much has to be milled.

Kon,
Its not worth it. YOu would have to flat mill them close to .070" to get them that small. Wont be much left of the deck if they are late model smog heads. Sell them and get a set of 64cc heads if thats what you need.

Ditto BillK. I doubt they could be angle milled that much if they are smog era heads that are thin. Add the added cost of angle milling, and it just isn't worth it. BTW, there are usually several sets of earlier camel humps and 041/186 heads floating around that can be bought for $100 or $200 a pair from people that have changed to better aftermarket or vortec heads. Something to think about if on a tight budget. :)

If you mill your heads that much you're going to have to mill the intake (going to be too tall to seal) ,need shorter pushrods,and have to shim up the distributer.
Aftermarket heads are going to flow better (most of them anyway) and be a better choice all around.