Widening a rear tub?

I don't see what the rear stays are going to do sat on top of the rear hoop, to be of any use in the event of turning turtle they would be better running down to the diff area where the chassis is stronger.

As for the back panel, well it was never intended to be used with the set up in the book....The Haynes isn't a "bolt together kit car" so having to make the odd bracket or change a few things is no real drama and doesn't affect your warranty as you don't get one if you built the car yourself