I have a 1965 reg A65 Lightning with an A50B.4**7
frame number and a A65 .D.C. 2**2.
engine number, on top of the inner timing case cover there is a disc screwed on with 7 & 10 stamped on it, as per picture below. I am not sure what it signifies, I have heard it may be something to do with the gearbox ratios but also heard mention it may have been fitted after bench testing.
Has anyone any idea what it actually signifies.