First thing to do was join my wood to make it long enough. For that I made up a saw jig which fits the wood inside tightly, with an 1:8 angle across cut to fit the saw. Pictures will explain it:
Below is the jig from scrap looking from above
This is cutting the scarf to make the join:
And below is a close up of the end result:
Once I had six long bits, adjusted the cut outs on the frame and epoxied three on one side all in together at once. What a nightmare trying to force three pieces together, bend them and clamp them by myself while the epoxy in the pot goes off. I ended up chucking most of the first lot of epoxy and having to make up a second lot.
This is the final result of the first one:
For the second side I have decided to change tactics. Seemed much quicker adjusting the cut outs in the frames, but I have the first ones to measure off to see how much to take off. Decided to epoxy the lowest one on alone first, making sure it follows the marks on the frame. The other two will then be dropped in together on top over the day or two when I get the chance.
From the front with the second side epoxied and clamped in place: