I've been offered a surface grinder

[Mayhem]

Thanks Sunset,

Interestingly the cross-sectioned pictures of the adaptors in your last link show a parallel section of the arbour, with a taper before and after.  My spindle is a continuous taper, as shown in my drawing and seen here in this photo:

   

Thanks Ken,

My adaptor doesn't have a keyway and my eyes deceived me when first viewing the picture!  I'm going to keep my eyes out on eBay but have other things to do before loading up with wheels.  That said, if a bargain comes up I'll likely grab it.