So having proved that I was correct in my assumption about shaped rear stays, I set about making them.
I cut a test shape, but forgot to allow for the extra clearance for the disc brake, so I started again. Here is the revised shape, with extensions to all the ends to allow for trimming. One thing I learnt from the www.plycycle.co.uk project was best to have too much and cut it back than not have enough and wish you had more. Its like any type of carving, or reductive sculpting, once it's gone it's gone. Having spent ages marking out the straight stays, I dove straight in, marked out the vital measurements and drew the rest free hand. I like the more organic approach.
Final shape with extension for disc brake clearance.
Having got the shape how I think it needs to be, I cut more. Four for the top ( the top stay is slightly longer at the top where the frame connects) and four for the bottom.
Here they are stacked up ready to be laminated together. I will go for West System epoxy resin again as I got to know its curing behaviour on the last bike. I have found that the local candler has started to sell it, so I won't have to trek across town to get it like last time.