Whilst you could say he was a Standard 3MT on the show, they were never LMS locomotives. Given his livery, I'd put my money on him being an Ivatt 2MT as used by the LMS. That said, I feel the 2MT is far closer to the one on the show.
I bought the donor model a few years ago with the aim of making him, but I guess I wasn't sure on how to go about it. The obvious modification needed was removing the top feed from the boiler, and this thankfully came off with a few scrapes of my trusty scalpel. I then sanded it down and got it smooth, before filling in holes left by the cuts.
The donor also had it's rivets removed, as these are not present on Arthur in the Television series. This meant sanding the roof, boiler and sides to get them flush.
A coat of primer later showed a few imperfections, although these were later sorted out. As he stands now, it's coming along nicely. Some transfer paper has been ordered so I can complete him as a fully accurate TV series model. Posed here with his wooden face, which may be thinned down so it doesn't stick out as much.
That's all for now :)