(https://i.imgur.com/3kHF8oU.jpg)
This is one of David Malton's designs available through his Shapeways shop. It fits on the chassis from the Bachmann N-gauge "Percy"
(https://i.imgur.com/jr7qI8y.jpg)
(https://i.imgur.com/wiY8eyu.jpg)
(https://i.imgur.com/qkxsHdQ.jpg)
The printing is in one piece; the cab roof and two couplings are attached by "sprue" and have to be separated ~ the detached roof allows for painting and detailing the cab interior.
There's not much to do to get a very nice little loco.
I filled the inside with as much "Liquid Gravity" as I could - I added too much into the underside of the boiler and found it fouled the little circuit board on top of the motor, so I had to unfix it - it sits "free" in the cab now!
I fitted a Greenwich coupling with loop at the rear, Crew from P D Marsh (via my box of people) Smokebox dart from Eilieen's (trimmed a tad) and home-made vacuum pipes. I padded out the cylinders with short pieces of tube.
David Malton's site is here
https://www.shapeways.com/shops/david-s-railway-bits (https://www.shapeways.com/shops/david-s-railway-bits)
(usual disclaimer)
Very nice Hugh - I must get on and finish mine!