I have driven the Mann steam tractor which is at Hollycombe. It is an interesting thing to drive, the same front end as the roller. I see that the safety valve outlet is beside the chimney on the roller, on most Mann engine sit feeds into the chimney, which is not helpful when blowing off as it draws the fire more. I have seen that roller at the Great Dorset Steam Fair a few times
I look forward to seeing your progress
Sean