I'm doing a little research on Model A stuff. Has anyone dealt with this company? http://www.code504.com/the-boxer-1928-1931-model-a-inner-channel-boxing-plates/
http://www.jalopyjournal.com/forum/threads/model-a-inner-channel-boxing-plates.962191/ Here's some reading for you.
I like those, I did basically the same thing on the last model A chassis I built only I made my own similar that out of 2 X 3 tubing cut fit and shaped to fit inside the rails. Mada a very stiff A chassis.