Back to the outboard engine stand - Castors were added. These came from Screwfix - I think it was a tenner for 4 and each has its own little brake lever. I also added an extra plywood pad across the top cross pieces just to strengthen the engine mounting area.
I won't paint it - not needed. Next steps - dig out the engine manual and read the servicing bits and then get the various oils and greases before we go into national lock down.
The plans I will re-post in the next few days with more accurate measurements added in.