The 7 dial speedo must be the most inaccurate speedo I've ever seen! I think that they all have issues in the 30-50mph range. Even the vauxhall Heritage Droop Snoot Firenza speedo needs some calibration as can be see from the tell tale stickers on the speedo showing the various speed limits which need to be adhered to. Although I think you could do something a bit more subtle.....
Personally I use my rev counter as a top gear speedo, my gearing seems to be about 20 mph /1000 RPM whit 225/50x15 rear tyres.
Editor of the VVOC Magazine ReVival
"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.