Cooper uses a picatinney rail uses when test-firing their rifles but for the life of me I cannot recall which brand. Give them a call (406-777-0373), I am sure they would be glad to tell you, then you could contact the manufacturer to see if they make a 20 MOA base.
An alternative would to use Warne bases and Burris Signature Zee rings with the +.20 inserts.
No idea on the bolt hole configuration question.
drover
