There are a couple of things I would like to point out, I see you are using the Bedford wheels..they are 10.5" x 20", the Dorchester used 13.50 x 20 or 14 x 20....much bigger.
I have quite a bit of info, stowage diagrams, and photographs of the drivers area. These were taken of the example at Duxford. I also have my own drawings in 1/35, as I had been gathering details for a long time.
Rivets.....have a look at my website
www.mooresmilitarymodels.co.ukI have a section on rivets, not the easiest of things to do, but it works for me.
I am sure that AA would supply the running gear and other parts.
Good luck with the project.
George