Rob,
Sorry I missed your post this long. Turning the propshaft with one back wheel stopped I came to 5.8, which dosent seem unreasonable when a 10/25 manual list top gear as 5.2. There is nothing in the 9/20 Maintenance manual I have giving diff ratio or gearbox ratios. A 9/20 having a lower numerical diff ratio , with less power would surprise me a bit, unless the tyres/wheels were smaller than the 10/25?
I now know the speedo turns/mile (2850 IIRC), and the alloy wheel that drives the speedo cable off the propshaft is stepped DOWN 4.8:1, and the tyres are 19x4.40; this gives a speedo cable turns/mile of (assuming 5.8 diff) of 870revs/mile. I intend to wait until I see what the speedo reads on the road before changing anything - the speedo people say they can splice a gearbox of any desired ratio into the cable if necessary.
I had an email response to an ad on Vintage drivers club recently, offering unspecified parts. When I asked what he had, responded with a picture, saying he was breaking that car up, what did I want. Sadly it was a picture of my car before I bought it, stolen off Flickr. Sent him off with a flea in his ear! Email was
eric53lawrence@gmail.com.
Thanks
jp