See PM, TerryP

It looks like the counter assembly from an Air Position Indicator Mk1.  The input of aim miles was derived from pitot (and static) pressure by the Air Mileage Unit then resolved into N-S and E-W in the API. Fitted to Lancaster, Shakleton, Varsity, Canberra etc. V bombers had Ground Position Indictors, similar electromechanical computing though.

Like most APs I’m pretty sure AP113 was amended from time to time and formed a list of Current publications rather than a list of all publications. Certainly the later catalogue of publications AP100Z-0101 was amended. However the DoRIS at RAFM may have a list anyway.

Chipmunk WP861 is still going strong in New Zealand:

https://rnzaf.proboards.com/thread/29198/prince-philips-airplane-flying…

Your ‘car’ insurance may cover third party claims for your trailer whilst you are towing it, unless someone knows differently.  Valuation can be contentious.  Public liability insurance can be difficult and expensive, I got cover by being a member of an insured society/group/club and placing the cockpit on formal loan to them for the period of the events that I attended. So join a group that has a policy if you can.

Here is a picture of the type 31 attached.

Here are some words and illustrations of the vampire system, although the reference numbers may be out of date. I see that the bottles were fired electrically by the pilot pressing a button in the cockpit, which may explain why it says “automatic”.

Gannet ?