I bet you're right. Fluid doesn't compress very well. Other people with ZE's in good shape have pulled numbers in the 200's-210's, from what I've seen. He guessed there were about 60k miles on it, said it was super clean inside and out when he got it. Apparently the manual tensioner is because the hydraulic one couldn't keep up with the new Interprep valve springs because they're so much stiffer than stock. I feel better about things now that I talked to him again last night.
Iirc, I pulled between 170's-180's on my current FS, burning oil and all. I was surprised, I thought one cylinder would be way lower, but they were all acceptably similar.