I can’t help you with value for a 2″ unfinished model.
The original engines were small and only weighed 3 1/2 ton. They were built to get around the road rules at that time when a man had to walk in front of the engine with a red flag and only travel at a max speed of 3mph. They also required a person to operate the boiler and a second to steer. A law was later brought in so that engines of 3 1/2 ton or less could travel thru towns at 5mph and not require someone to carry a red flag, and only needed one operator. Unfortunately they were too small to do any decent work.
I have built a 6″ scale Ruston Proctor SD. Build details here:
https://www.model-engineer.co.uk/forums/topic/6-ruston-proctor-traction-engine-model-build/