The class 16s are quite different from the 15s. They are slightly longer, a longer wheel base, bigger spoked wheels, and the sole bar is higher up. I dont think there will be much they can reuse off the 15 model.
The new engine is an ex class 15 lump. IIRC its ex D8217 when it was new. The only non orriginality parts on the 15 will be the control gear as it was all lost when the loco was a Crewe. Replacements have been sourced from class 31s thanks to a very kind Mr Needle. We do have a set of correct BTH traction motors to replace the missing ones.