Gordon, I am using ITG foam I got from Ray at RD. Works well so far, but only ~2,000 miles on since re-commissioning. The red plastic holder seals well to the back plate. Foam appears to be of good quality; way better than the foam dome deals I had from the PO. I mounted the ITG upside down to put the closure tabs at the bottom to prevent fouling the bonnet. Overall, pleased with the kit.
Although I have SU's on a Stromberg head, I expect this set-up would work fine on Weber's. I ordered my aluminum backplate without holes cut, so I was able to be sure I could fit to the SU's. Ray also lists cut back plates for Stromberg and Weber/Delorto. Three different filter depths (2 3/4" to 5") are listed if you have clearance issues, perhaps with RHD? I managed to originally mount mine a bit higher than ideal for bonnet clearance, but have since adjusted things; measure once and cut twice I guess.
You can find a picture & prices at rdent.com under Europa Parts about half way down. I couldn't see the product under Elan & Plus 2. When I spoke with Ray about them, he mentioned he brought them in for the Europa TC; think I was the first he sold specifically for a Plus 2. Perhaps they fit right side up on the Europa.
Let me know if you want a pic of my set-up on the Plus 2.
HTH - Just shifted to fourth gear!