Dean, check out this pps. And as others have said in other "leaning"
threads, check out John Deakin's articles on avweb.

http://www.avweb.com/other/Leaning.pps

Without an electronic engine monitor in our Aztec, I usually lean to 75-100
ROP using the EGT and sacrifice some fuel. My primary goal is to keep our
CHT below 400 and the oil temp below 200, using cowl flaps as necessary

Jim
..