Thanks Sparky and Steve,
I had found the Rider tv Index on the ETF website and saw they listed a revision for the 28f20 chassis in volume 3-1. I hoped that was the change in schematic I was looking for.
http://www.earlytelevision.org/pdf/riders079.pdf
Sparky, Thanks for the Bietmans scan. Does Bietmans list any revisions for that chassis?