Seat dimensions

Thanks Geoff that is just what I needed

This has raised another problem. My 1971 Roadster came to me with an additional Interstate steel tank to replace the fibre glass Roadster tank which, along with a non Norton seat, is not in good condition. I have tried the Interstate tank for size and fits and looks well, however it so much longer than the original tank.  I was hoping that a standard Roadster seat would fit but alas no. As Geoff has pointed out the distance from the nose to the mounting brackets is some 15", but I need a mounting distance of only some 11". Would a standard Interstate seat fit?