The final overalls for 2WD & 4WD are on the Stotfold site,
http://www.stotfoldmcc.com/results/4wdoverall2012.htm
http://www.stotfoldmcc.com/results/2wdoverall2012.htm
these may be of interest to all racers.
2012: 87 racers in 4WD & 134 in 2WD - wow!
(2008: 47 in 4WD & 49 in 2WD)
not sure how the grades are worked out.
Edit: (Same) Formulas for 2013 list now added to Stotfold site: http://www.stotfoldmcc.com/files/Formulas_2013.htm