Just got a 17 from Modelfair- Heljan 1701 with replacement chassis (no. 8561).
Its a little noisier than the Hymeks and Birmingham Sulzers by Heljan but you can reduce the noise by taking
out the piece of beige plastic- the cab interior- and putting crew figures in to disguise the mechanism. After
using an R8249 chip the beastie runs quite well, although not fast, but quietish.
The prototypes were not that fast- you could use an older chassis
and remove gears and motor and run as a dummy. Seen quite a few photos of them in pairs-especially on passenger trains- summer only and usually excursions