Didn't mean to veer this thread off into talking about Wankels, though it's a interesting topic. I was just picking an example of a tough application for the typical commercial test stand.

I went back and browsed the PSP website again, and sure enough it does have an optional rear mount plate.

Another reason I like the 2x4 blocks is that I end up with engine stands on which I can rest the engines in my workshop, even with a prop attached the engine. I got tired of engines dripping oil and dentingthe drywall surface of my building table. BTW, on engines larger than .46 size, I typically use 2x6 block instead.

Also, the flexibility of sawing and attaching pieces of 2x4 also allows me to mount tuned pipes and secondary mufflers (to minimize the neighbor annoyance factor) at will on the same sawhorse.