David:
I found two Youtube videos showing three methods (two manual methods) for locating holes. I just thought I would pass them along. Since I don’t have DRO’s, it looks like I need to get a height gage. This guy is pretty good – you can tell he’s spent alot of time teaching too. 
http://www.youtube.com/watch?v=t6evpRPPlrY
Thanks!
Tom