The Whitby branch is mainline, whether you want to admit it or not. It's still NR controlled infrastructure. Ask the Northern drivers how they feel about driving down there.
7628 is TPWS fitted, which it requires for Whitby - Battersby. It lacks OTMR, which it would need to venture further afield. 7 Mk 1's to Battersby is a pretty good work out for a little type 2, so definitely worth a look if you like the things. OTMR would cost several tens of thousands of pounds, so if you would like to stump up the cost.....
9F's - The issue is most definitely flangeless centre driving wheels. They are much wider than conventional wheelsets, and the concern is them hitting modern raised check rails, and some forms of high speed crossing nose. However, enquiries are evidently going to be made re 92214 & Whitby after its next overhaul, so there is some hope.