Cheers Phil - I was comparing your resto picture to one that I found on ebay. The ebay one is pretty unclear although it appeared to have an odd attachment in the seat area.
I've now found a further piccie on the US site which shows the frame behind the tank / engine and also the shock mount. Logically, the Custom frame continues downwards from the headstock and then rises back up with shock mounting points higher than the riders seat rails, and the pillion seatrails higher than the riders. The odd
Yours levels out behind the engine / tank and runs horizontally to carry a European style seat...that's what I need so problem solved!
thanks.