These are the later A+ type spec which rover superseded to when upgrading the idler gear material on injection cars. See workshop manual for shimming details
Quantity required is 2 per gearbox but the idler gear requires shimming for correct clearance 3-6 thou as per workshop manuals but 3 thou for road and 4 thou for race is found to be reliable see following:
DAM4822132-133"
DAM4823134-135"
DAM4824136-137"
[link]DAM4825[/link}138-139"