Hi Bruce,

In reply to post #73 I would delete the box section and the 2 angle sections. I would then replace them with either an RHS (rectangular hollow section) of similar depth to the plate, or stack one box section on top of the another and bolt the rails&plate to that. Looks like it would be a reasonable fit based on your drawing.

With the RHS option you could potentially delete the plate, but I think on balance I'd still leave it in.

Hope this helps,
Barry