Aircraft are just a machine. Made up of various components. Often in the case of GA aircraft there is nothing too special about them.
Sure many of the components are sourced from the same suppliers as other industries. Bearings, light bulbs, electrical components as mentioned earlier, can be identical. Often they are. It is the next higher assembly that will differ, sooner or later.
The boat outboard motor hydraulic pump on a Piper Arrow has to be different somewhere. Indeed we can soon see that not many marine products use Mil Spec 5606 fluid.. maybe that could be an important difference. Same with brake components. I guess what may often look identical may just have some important subtle differences, - the changed part number may indicate different seals have been fitted.
The electrical system on some GA aircraft does use identical components to those fitted to other vehicles. The electrons are the same so yes, - it may be common to see inter-changeability with the component. The overall system may well be different.... as I believe they are.
Cars simply do not require an alternator field switch. They may not have an Overvolt relay added to the circuitry either.
That said, many automotive electronic regulators worked much better on the Cherokees and the Islanders than the OEM products... remember electronics changed a lot during the 70's.
The regulator generally just varies field current in response to alternator output voltage (bus) when all said and done. I am sure many here would have experienced the fluctuating needle movement in some of the original Piper ammeters (loadmeters).
I don't recall the R22 transmission.
I do know much (too much !!) about the R22 drive train failure of the one out of Nelson seven years ago. It was the owner who demanded an incorrect Dash number part be fitted. Saved him a Dollar but cost him his life.
Some guys really do have that mentality...