Paul,  according to this article, we might be able to put lightening
holes in all four faces of the s-beam.  Of course,  some careful
layout would be required where the thru bushings are installed.
Jerry

http://www.autospeed.com/cms/A_2828/article.html

What the article does not say is it affects the stiffness of the part.
I think we should stay with what we have. The top and bottom walls
of the Schertz beam are the most important parts. The depth of our
beam could be deeper if we did away with the bottom mounted rad
in all cases. However the clearance it provides now is critical
in tandem airplanes both pusher and tractor with rads mounted under
the engine.

Paul Lamar