AJS M20 timing cover removal

[Brad M]

Hi All
I am just trying to remove the timing cover from a (new to me) 1954 Model 20 and have hit a snag trying to remove the fixing just above the oil inlet - see photo below.
Instead of the usual screw this seems to be a stud and nut. Is this usual? Also does anyone have any tips of loosening the nut? I don't have a socket thin enough to get in there - the photo is deceiving as the curvature of the recess prevents the socket going in far enough to engage the nut. I am at a bit of a loss.
Any advice gratefully received.

[Groily]

Should be a 2BA screw like the rest, but because the threads get worn over the decades, this area can become Bodgeville Central -there are quite a few studs 'n nuts using oversize threads, etc, out there.
Thread trouble here is regularly caused by overtightening socket head screws, so a correct set of deep-head cheeseheads from the Club (and gentle hands) is a good investment if the rest of yours are 'wrong'.
Can't really see what the size of that nut is, but a ground down small socket will get it - the PO must have managed to do it up with something!

[Brad M]

Thanks Groily - that's very helpful.