Here's a thing to try? Hare Scrambles.

[BLINGMW]

something cheap... i'd even rock a YZ85. I need to read the rules and see what "class" fat guys on little bikes fit in.

There's age based classes (30+, 35+, 40+) where you find the largest mix of bikes and you could certianly run an 85 (80cc minimum) and probably still not finish last. And the sportsman class where you don't even get a number or finishing place. But in the more competitive classes, the smallest is an up-to 200cc 2-stroke / 250cc 4-stroke class. Then there's another one for stuff over that. So no serious poky classes (unless you're 15 years old or less).

I'd probably still set it up for motocross but I don't see it being a negative factor. Most of my younger riding was trails exactly like those. So maybe some handgauds that I can pop off for the motocross track and go for it.

I'm sure it'd be fine. That's where my co-worker started on his 250 2-stroke Honda though and ended up softening it up a lot from a motorcross setup. There's not really jumps unless you seek them out, but the terrain is a mixed bag of god-knows-what. Then yes, handgaurds and radiator guards are pretty much a must, and then you see others with various other skid plates, brake gaurds, cables and other gaurds to keep branches out of pedals here and there. I also read a discussion about o-ring chains, which most recommend as the lube on a regular chain doesn't hold up to all the dirt and mud for 2 hours so you'll be replacing it every few races.