yes totaly agree, mite be worth getting intouch with DRC and see if they have any photos of Pendennis in service for the period you are modeling, however in 4mm oogauge you probably wont need to modyfy the frames inless you realy want too, but other details obove the sole plate would be more obvious therefore should be changed as appropriate to that loco at the time period given that is of course if you want to go the whole hog as it were to make the engine completly correct
hope it helps