Got no idea what it is from D.
I wonder if it is from something similar in size?
 
4 wheel motor bike? Snow mobile, golf kart etc.

Yes found the Golf Cart axles seem like a good fit
gotta find one with a big enough motor on larger
4-6 seater golf carts for big hefty people.

The other puzzle is Aussie Race Cars using the
venerable and common FJ1200 air cooled engine.
Need to find out if any changes to the sump are
made to be able to use the engine north south
rather than east west as on the bike it came from.

I suppose bikes have more Gs than cars when accelerating
and braking these earlier engines are fairly well build by
Yamaha hence the chosen engine for Aussie Car Racing.

here is the Engine description from https://www.aussieracingcars.com.au/about/faq

""The 1.3 Litre 16 valve, twin overhead camshaft engine produces 135BHP and is factory fitted by Yamaha with all the go fast goodies including forged slipper pistons, light weight conrods and double valve springs etc. The engine propels the car with exhilarating performance and requires no further development. The smooth and wide power band of the engine allows the car to accelerate well from low revs which is great for novice competitors right through to seasoned experts. The engine is sealed on delivery and the category rules are rigidly enforced.""

I will see if there is a Nazibook link for the racing guys havent been able to find a forum yet.

https://upload.wikimedia.org/wikipedia/commons/thumb/7/7a/Yamaha_engine_in_Aussie_Racing_Car.JPG/800px-Yamaha_engine_in_Aussie_Racing_Car.JPG