Paul,
On the narrow stand the lower part of the legs are parallel - on the wider stands (there were 2 types) they are splayed. The standard set up for the stand pivot is: a 1/2" dia pivot bolt through the frame lugs, the stand has a bearing tube 5/8" OD and a neat fit between the frame lugs.
The most common problem with Mark stands not supporting the bike is due to owners trying to kickstart the bike on the stand - the extra load wrings the frame cross tube, making it difficult to remove the pivot bolt as it then fouls the bottom frame tubes. Because of this problem, Club spares used to supply a stud and 2 nuts in lieu of the original bolt and 1 nut. If your cross tube has been wrung, but you can still fit the pivot bolt (stud), the stops on the stand can be welded up, but dont attempt to start the bike on the stand or the cross tube will get wrung even more, making the pivot bolt impossible to remove. Some frames had steel lugs for the stand - others had bronze lugs, but in both cases, the lugs were pinned and brazed to the cross tube.
Regards,
Eddie.