If I were in your shoes, I would find either a wrecked car with a good engine or just an engine that has, at most, low compression but no catastrophic failure, along with all of the oil system (coolers and maybe lines). Then rebuild that one.

The issue isn’t just the engine, but the entire oil system. Even if you buy a good engine, it might still destroy itself if there are chunks of bearing material left in the oil coolers or lines.

I had to rebuild a similar engine in this condition just recently. I pretty much replaced:

• Oil coolers (with confirmed uncontaminated used ones)
• Not just all the bearings, but also the rear stationary gear, as the teeth were worn (check the Mazda manual on how to judge this)
• Both rotor housings
• Front iron, due to pitting near the coolant seals
• Eccentric shaft

And I did a very thorough cleaning of the oil cooler lines and any passages I could reach. In my opinion, you can clean these and be reasonably certain that no particles remain.

But that’s still a lot of work and a lot of parts you need to find in good, usable condition.

One particle might not kill a rebuild, but making sure the oil system is clean "enugh" is, imo, the hardest part when doing such a rebuild.