Hi Henry. You are correct, it should be there. It is trapped between the crank and drive sleeve, and rotates with the crank.
From your description you have an early Longstroke engine, later developed so called shortstroke design has a roller bearing. The shim you describe is part 67 389 *and although listed as a shim, is more of an oil slinger. It was also used on the later engine until the advent of the oilseal design change, and so can be seen in 1949-53 parts lists. These earlier engines don't have an oilseal, but the drive sleeve has a grooved periphery to act as a scroll to hold back the oil. Having said that, many engines are found with a smooth edge drive sleeve, identical to that used with the seal. Your hole in the case where the drive sleeve goes should be a close fit to the sleeve edge.
Out of interest, did the ball race stay on the crank or in the case? The later design is certainly easier to pull apart, but having a ball race avoids the usual hassle of setting the crank end float to the fine limit required on the later engine.
Plenty about this shim on the Forum, just a case of going back thro' previous posts. Parts catalogues are also listed in the Literature Section of the Forum.
Swarfy
* Typo Error Should be 67-349