Wagonman
Western Thunderer
Wildly
Does this help?
http://www.rmweb.co.uk/community/uploads/monthly_04_2013/post-17793-0-94377100-1365330268.jpg
Best
Simon
Unfortunately that's an O1 not an O4. Willy was correct in his surmise that the shirt button went on the triangular pace between the LH and Centre doors. Nos 1868 and 1870 are definitely recorded as carrying the shirtbutton roundel though no doubt there were others as well.
Oddly the HMRS Siphons book doesn't give any tare weights so far as I can see but Russell (Vol 1) has a GWR drawing which gives average tare of 10.11.0
And that's the unvarnished truth...
Richard