I have an Air Britain sheet Drawing no. AW13 dated 19/9/55 which has the dimensions of 4 different styles of EJ triangles. It lists them as having been used on SeaHawk Mks 1,3 and 4. Also they were used on Hunter. Venom, Vampire,MK1 Vulcan and others.
It states on the sheet that some slight variations may exist as they were “hand painted,stencilled or transfers.
If you think it will help I will be more than happy to send a copy.