I did contact Keizer wheels directly to see if they had a record of the sale that would have the exact measurements for the rims I ordered. The sales guy was on the road and didn't have access to the records until monday but thought that it wouldn't be a problem finding out that info. I do know that the back rims (because they are off the car right now) measure 4 1/4 in from the mounting surface to the back lip (turn up point that holds the tire on the rim) The front rims are different.
FYI I had to have a little machine work done to get center caps to fit and to fit over the center of the spenal mount but this could have be done by Keizer if I would have thought of it before hand.
I don't have the exact measurements (or the tools to measure it exactly) but my eyeball measurement is 2 1/4 hole on the backside and 2 3/8 on the front. It might be better to send them a old center cap and have them machine it from that. I also had to have a groove machined in to keep the center cap "snapped" in. Drop me an email at email@example.com if you have anymore questions. I'll give them a call next monday and post the exact offsets and widths.