compression ratio

Yes, it will drop your compression about 1.0-1.2 points.

However, I caution you on using the "book" numbers. Measure what you have and calculate from there.... I have found that the book numbers do not match up. I tested a set of 67 318 heads that are supposed to be 57 cc's and they came out to 63... Not as much improvement as I expected.

Here's a thread to help you calculate the compression on your parts:

http://www.forabodiesonly.com/mopar/showthread.php?t=278215