This is an
Atkinson-Walker Class A.3 engine. Only a small number of these types of engines were built. The best know and long lived of these being the County Donegal railways diesel conversion “Phoenix”, now housed at the Ulster Folk and Transport Museum.
This is a 3 mm scale print in Smooth Fine Detail Plastic and designed to run on a Tomy-Tec HM-01 chassis. It is printed in one piece, to be separated in the building process, roof, body/footplate, and detail parts; these include work lamps and basic couplings. If you wish to know how similar models were built you can see this on the Model Engine Works blog at: http://modelengineworks.blogspot.com/2018/04/atkinson-walker-steam-tractor.html
There are some alternative chassis with a 16mm wheelbase available at the site below.
http://www.narrow-garage.com/NarrowGarageE.html