After a lot of discussion, advice and thought I've gone with the plans 2024-T3 aluminium for the engine mounts. However they are 1.5" X 1.5" instead of the plans 1" X 1". All well and good but I will have to trim them for the lower mounts for a good fit and we will see how this works with the cowls too.
Pic 2 shows that they are not a 90 degree extrusion! After some online advice it seems I can live with it but I am still unimpressed given this is supposedly aircraft quality material from an aircraft supply place. In practice the mounts bolt on towards the bottom of the join and even with a light clamp they come together easily enough.
Pic three shows that I've done a little join work and countersunk some screws per plans.
