Hello
i would suggest a Graham ind. TVR1A kit, it can be easily converted to r/c. I bought one in kit form and its pretty easy to build with minimal of hand tools and requires very little lapping(the messy part of the deal).
you can attach a servo to the steam valve which also acts as the reverser.
I am currently building a live steam shay loco in 1:22.5 scale using this marine engine. The only problem is you would have to build your own 45psi producing loco or vertical type boiler.
Here's the link
http://www.grahamind.com/tvr1a.html to their website.
I have also done some commercial batch runs of a coal fired 5 inch gauge 0-4-0 Hunslet loco capable of hauling 3-4 adults. but for producing those i use the facilities at my garden railway manufacturing workshop in Calcutta.
Attached is a photo of the same.
Regards
Nilanjan paul
www.pline.in