Thank you!
Ragdoll and baking skeletal characters would be more accurate and look better, but I was worried about performance and high draw calls with thousands of uniquely posed bodies. Luckily the Synty Kingdom pack already has a dozen 'dead soldiers' in different poses. I just physics simulate small groups of bodies, then bake the transforms and do the next batch. With only 10 unique meshes, the bodies are instanced/batch rendered and performance is great. Only took an hour to fill the level with 3000 bodies.
Here's a clip of the process: