Originally the stand had a steel sleeve 5/8" OD x 1/2" bore and a 1/2" dia pivot bolt. Now, quite a few owners found that if the bike was repeatedly started while on the centre stand, the frame cross tube that carries the stand lugs got twisted to the point that the pivot bolt could not be removed, as it fouled the bottom frame tubes. The usual dodge to get the bolt out was to saw off one side of the bolt head. With this problem in mind, Club Spares used to supply the 'bolt' as a stud and 2 nuts.
If you do get your stand off, it will pay to check that the lugs are not pinching in on the sides of the stand. If they are, carefully tweak them out to give some clearance (care will be needed as some frames had cast bronze lugs) and then make up a new spacer tube to suit, so that the 2 lugs and the tube can be clamped up without binding against the side of the stand - then refrain from starting the bike on the stand!