My rev counter over reads by at least 1,000rpm at cruising speed, and my clock like yours has been repaired and remains accurate twice a day.
I have seen this site:
https://www.clocks4classics.com
which claims to offer electronic conversions for the clock and rev counter. The fitting instructions for the clock kit are 20 pages and involve the total dis- and reassembly of the clock mechanism. (They do offer a fitting service.) I have no experience of them myself so cannot vouch for its efficacy. I have considered doing battle with my clock, but after twenty years I'm quite used to it always being ten to two when I'm in the Bristol.