I've replied by PM, I'd need the two dimensions external and internal recess, however I don't like the idea of butchering a Gandolfi back or I'd have done this myself
A couple of years ago I made a 6x7 back for a MF field camera I built, that included the GG screen hold etc. It wasn't difficult would have been easier if I had Alan Clark's wood working skills and tools though.
I shot quite a lot of Harman DPP last year and took copious notes. I'll see if i can dig them out and let you know how I went about it. There was definitely pre flashing going on with a couple of layers of white paper.
Any notes would be useful Brian. I have a few boxes of Harman Direct Positive paper including some of the RC version which was only successfully coated once. The second coating run failed and had to be scrapped and no RC DPP paper has been coated since.
OK, looking at my notes, I rated the paper at ei 6, metered the scene then preflashed through a double sheet of Hobbycraft tracing paper at 3 stops under then shot again at the metered exposure. This certainly cut down on the contrast. I'm going to buy another box and have another go now that I have access to a proper darkroom and not just some developing trays in a bath!.