I don't have a model site for you, but here is a prototype site with heights for lots of rail weights. At the bottom of the diagram, you can step to the right for heavier rail and to the left for lighter rail.
O. K., thanks! I've found a wealth of information on O scale in the NMRA's Standards and Recommended Practices. I should have remembered that most everything I might want to know will probably be found at the NMRA's site.