The flanges are a bit messy, three different parts. You can make your own based on visual inspection, they just need to fit inside the cylinder exhaust port with a sealing o-ring. This can probably be one piece instead of the OEM o-ring and gasket (27 and 28)? Then the outside bit then just needs to accommodate the JL flange. That said even getting those parts to fit still means the mounting holes on the chassis likely won't line up.
It may be easier to do away with the flange and see if you can get it to fit in the same way as the Sugo pipes, ie, directly into the cylinder with an outside o-ring and some suitable bits that slide over the JL's? Maybe mount the JL's and see where they end up in terms of distance to the cylinder and work from there?