Milling 587 small block head?

I have a low compression 73 340 and was thinking of having the heads milled to gain a point of compression. My question is has anyone know how much is needed to be milled to gain a point assuming they are at say 72cc now? I will have the heads cced and measure how far down the pistons are to get my compression ratio to
Start with, I am hoping it is at least 8 to 1 or higher. I have no idea what pistons are in the motor, it was a stock rebuild when I bought the car. Just trying to get an idea of cost from the machine shop.