Ill try to find the model
But as you write it schould be for one of those models, but see the link i put in it says it covers them all, but it does'ent say how the electronic tach work, I found one some time ago with some more info on the eletronic but nothing useful
http://static.summitracing.com/global/images/instructions/atm-6851.pdfHere is the other instruktion. but it is worthless
http://www.autometer.com/productPDF/1244.pdfBut It schould be the 6854 model