Just for correctness, the Ordnungspolizei was abbreviated in the typically Teutonic way to Orpo (OrdnungsPolizei), not "Oper" (which means "opera") :-)
There's a thread on this site about the J60 engines, Robert:
The engines do appear to be interchangeable, and modifications made to military versions seem to have been incorporated into versions for the civilian market.
I'm actually really pleased to hear that, Jon... I know you considered using some existing track from e.g. a BMP, but I suspect you'll get the best, most authentic result by fabricating the links yourself.
Good info from Le Prof there.
Also, the use of full stops after acronyms (e.g. "U.K." in this instance) had fallen out of fashion in British English by the mid to late 1980s. Maybe that'll help you get a bit closer to the date of manufacture.
I don't know whether you've seen this (e-)book before, it specifically deals with Wehrmacht vehicle track structures & designs - perhaps it would be of help?
https://www.amazon.co.uk/Panzerketten-Gleisketten-deutschen-Kettenfahrzeuge-Weltkrieges/dp/3943883000
It's in German, but I'd be happy to translate any specific sections for you if needed.
Hydraulic hoses can delaminate internally, preventing a return of fluid from the callipers or slave cylinders. That would jam the brakes on.
It's a fairly common problem with old brake hoses.
The camouflage pattern on the "turtle's" head suggests WW1 German army to me, but that could be way off the mark.
I'll hazard a wild guess: is it a booby trap device, similar to the dead rats packed with explosive that commando-type units are said to have left on German bases?
Or a camouflage helmet for commando-type units approaching enemy formations in water?
The speed claim isn't necessarily incorrect, I remember reading about T.E. Lawrence (of Arabia) speed-testing 4.7 ton Rolls Royce armoured cars in the desert at over 70 km/h.