As and whenever mate - the route I'm thinking of probably wouldn't take more than an hour or so, provided the access at the end of it is open - if it's not then reversing the 90 back up a couple of miles of lane might prove err... interesting.
It's roughly equidistant (North South) between Chobham and Trottiscliffe - easy to spot on an OS Explorer as it runs through an area labelled on the map 'Bowling Alley'.
MHM and Marcus might be coming down this way in the not too distant and we were going to have a look at it. If there's less than 4 vehicles going I'll drop you a PM if you like.