Thanks. Found that with a google search right after posting. :D
I think I could make this work with some plates welded onto each side:
http://www.welderseries.com/blog/online-store/c-notch-fill-piece-rear/
Cool. Looks lower because of the Dart 1/4 covering more. What do you have for springs? There's guys on here going wider than 325. It could work without much trouble.
I have to see what works up front without a spendy solution before I finalize a plan for the back, but I'm thinking seriously of doing the C notch. I'll look at your thread again to see how you managed the front end.