A very interesting line up Daniel, you probably can tell which one is my favourite.
I've only ever owned one aero IC engine which was made by this company which are happily still in business:
https://www.eifflaender.com/engines
I no longer own my little P.A.W diesel engine (i sold it to fund a steam purchase) but it was full to play with if a bit messy.
Wow Philip ... what an interesting and relatively old company, and might I add, fine looking engine line. Never heard of them myself, but then they are an ocean away and I was dealing with a rather parochial, standard American market back in those days. Thanks for the link.
I can only guess which brand of my engines finds your favor (Fox perhaps, yes?) ... but I must say for simplicity and reliability they were our go to engines, and I have a true fondness and respect for them!