Wow! I'm really impressed by the old-maps.co.uk site. Thanks for the link :-)
Sadly there was nothing marked on the 1887 map, of course if there was a small henge there it doesn't mean it was necessarily sufficiently extant to in the 1880s to be marked on the map. I'll head up there later today or tomorrow and take a few more pics to see what other perspectives suggest. Maybe it'll be excuse enough to produce a weblog page.