Standard 72 4/4 will have the 4.1 axle, and 17.5 mph per 1000 is exactly 70mph at 4000rpm.
I did all the maths in the early 80's and have not forgotten the answers. I fixed it, but my 4/4 speedo drive had a problem (glue to the rescue!), and later the speedo (repaired with bits from a Jag speedo I bought from an autojumble) so I did for a time need to know how many revolutions was a certain speed.
