1938 Model 18 Prop Stand

Have you considered the Vintele stand? It's suitable for rigid frame.

.... in the spirit of Titch Allen's bodges, use a Kawasaki one as mentioned here several times. Like this:

... the front engine mounting would be very similar even for the open frame. The one I made (adapted from a set of alloy plates I had lying about) was easy enough to fabricate and only needed a couple of studs and spacers to be made up on the lathe.

I have no experience of the Vintelle stand  only to observe it is a period accessory  which might or might not be a reason to fit it.  It is adjustable for uneven ground  and appears to be easy to use..if you don't want (or aren't able) to pull a heavy bike onto its rear stand.

.. are readily available from ebay for £10 - £15. You have to make a few easy mods such as removing the switch mounting.