Hi Hob.
No, couldn't say for sure if the stones are sarsens - though they look like they might be (and there's that local story that they were brought up from Wiltshire). The idea that the Romans might have had a hand in them is interesting. Seem to remember reading they were in the area (and there are the Bartlow Hills close-by that, though classed as Roman, might have been built on pre-Roman tumuli.
Welcome to the joy of prehistoric rock art. The level of uncertainty is a crucial part of the fun ;)
Aye, can see how addictive it could become. Must be fantastic to turn over a turf and see one that no-one else has seen for centuries. 