On the subject of starting aids, I recently swooped on an original impulse coupling, still attached to a Simms SR4 X on eBay. The asking price was horrendous but after some serious haggling (and no other bids !) I managed to cop the lot for a realistic sum. Unfortunately, the mag armature has 'semi toasted' sometime in the past and the bearings are completely knackered but there are many good parts to be harvested. The prize find is the impulse unit, marked 'Type X' and apparently in good working order. I will add some pics.
One puzzling thing is the apparent lack of any means of lubrication for this item. Later versions show an oiling tower with a sprung lid, but there is nothing on this one.
I am now looking for a 19/20 tooth Simms rubber vernier coupling and a 19 tooth backing plate with clamp, to complete the ensemble. All this is required for a new Thornycroft J Type project, recently acquired from Australia of which more later.
Tomo