This is basically what we did with Mark's back end
when he first did it, we just made the chassis up to RS14, then extended backwards 230mm. This section is 100mm short of each end to allow for the radius on the tub.
Can be seen here on Layotn20's chassis, which is the one we originally made for Mark (aka Fabbyglass, Triton Race Products)
http://www.haynes.co.uk/forums/attac...8&d=1273428132
Kind regards
John