Some additional info for you:
HMRI = Her Majesties' Railway Inspectorate (or single inspector may also use this abbreviation)
Act of Parliament date for building the Ffestinog Railway (which uses the Anglised single F, by the way) in 1832. The first two locomotives date from 1862/3 (named The Prince and The Princess)
The American built (1916) loco is "Mountaineer" which is currently stored, as the boiler certificated expired in Feb 2006, awaiting resources for her overhaul.
Just ask if you want more details - I may already know the answer.