Mijostyn
I am trying to figure out how crank shaft bearings , mains or rod, have anything to do with plastic tone arm bearings. Automotive crank bearings are designed to take a pounding and high rpm. They are made of various metals and are running in a oil bath to maintain a certain tolerance and lubrication. A tone arm never does even 1 rpm or takes any pounding. There is no real weight so you have gone from one extreme to another.
This whole tolerance thing is easy to measure and talk about but in the reality of a tone arm how realvent is it. Now in vibration control we may have a whole different ball game. But there is not a consensus on what should be done here, even by experts.
The only issue I would be concerned with would be long term wear in the small area of movement. Ok maybe long term stability of plastic just exposed to a indoor environment.
The sad reality is there is no one size fits all in audio. This plastic bearing could work great in various tonearm or not. So we are back to build it try various bearings and listen. Then you at least know in that arm and system YOU like one over another. Or maybe no difference at all.
Enjoy the ride
Tom