Hi Joe ,
Not many of the Stuart engines were based on particular full size engines so exact fidelity does not apply in their restoration .
Generally a clean and tidy Stuart engine will be worth more than a tatty one but not always by very much and selling prices on some sales sites defy logic altogether .
I like to see this sort of engine just in basic workshop condition – working properly , bare metal surfaces clean and nicely finished nut not over polished and plain paintwork .
Stuart engines were often painted grey or green for display .
Full size engines were painted and finished in every way you could imagine so just choose scheme for model which is pleasing to you .
In older times workshop engines were often kept clean and in working order but not specially fussed over – to people of the day they were just ‘ electric motors ‘ that you turned on when needed .
Generally in full size only engines like Mill and pumping station engines had special treatment .
Regards ,
MikeW