AJS & Matchless were totally different in the prewar years. In the very late 1930's some parts were common to both marques. There were SV, OHV, OHC & v twins all quite different. Oil never went to the rockers until 1939. Although AJS had oil to the enclosed rocker box in 1937. Crank cases varied in size. Pre 1930's oil was mainly hand pumped into the engine. So very few of the prewar era bike's would hold the same oil in the crank case, to compare with post war machines.
http://archives.jampot.dk/book/Owners_m ... Manual.pdf
The above is a very good manual to refer to for owners of post war singles. It explains oil circulation in detail, inc the predetermined level in the sump. It does not state how much oil is retained in the sump. It does say why it is needed. Data is also useful, as it gives sizes etc The WD parts lists also gives many part dimensions post 1951 parts lists do not show. Again useful to post war machines using the same parts. If the post war machine in question is post 1951, you will need to convert the new pt. no. to the old pt. no. To make use of the more detailed old parts lists and WD manual in the above link.
Quite often I may answer a question here on the forum. Not because I know it all, it's because I do know where I may be able to find the answer. You will at least need to have the books on your own bike to start with. Then refer to a book like the 1954 new to old part number conversion. If your new pt. no. converts back to a old number, you know you may find more info on the part in an earlier book. Just have a look at "data " in the book via the link above, also lubrication, which will tell you where oil goes and how it lubricates your whole engine before returning to the oil tank.
) if when next changing the oil to run th'engine and measure the oil drained from the crankcase, after waiting say 20 minutes or so for the warm oil in circulation to drain down from the rocker box and cam chest. I believe this figure would be relevant to all post-war H/W singles (maybe some pre-war as well, Rob?). As far as I know all post-war single engines share the same crankcase.