BTW, my old Saturn was over 200,000 miles before it was opened up, and then only because of a busted timing chain guide. At the end, somewhere over 260,000 miles, the odometer was broken. People I've spoken with said these cars kept going for a very long time; mine certainly did.
My car had the SOHC engine. Wikipedia says it weighed 197 lbs or something like that. I think it was supposed to have 85hp. A later SOHC engine made 100, and the The DOHC makes 125 horsepower, but is slightly heavier. However, I don't know if those had the same reputation for reliability. I think that figure was with all the junk on it! Swag Automotive sold an aero conversion with a PSRU, but, given how the owner died, it might not be a good idea. He was flying a Varieze with a converted and apparently hopped up Metro engine in it. Never got enough power to climb over trees at the end of the runway. Verdict was severe preignition. Or at least that's the rumor.
From looking at a torque curve, it appears my engine (or possibly the 100 hp version??) would get 50 hp at 2500 rpm. The DOHC would get a bit more. So maybe on a Piet you could get away without the PSRU?? What happens to engines like this if you run them at high throttle settings and 2500 rpm?
A further consideration for this and other more recent auto engines is that, from what I've read, lead kills oxygen sensors.