Hey Refer John-
I was talking to my friend who runs all the D36 family enduros, and has ridden and set enduros for a long time. He said a couple things that I'll pass on:
Cow Mt. isn't doing a family enduro this year, they're only doing the championship enduro. First enduro is at Hollister. My friend advised against trying the cow mt. enduro on a xr650l. Strongly.
Second, not sure how often this happens in other areas, but it does happen here: Course mileage may not match your mileage at times because the organizers can adjust mileage to make a certain checkpoint work. Checkpoints can only be at certain mileages so that it falls on a minute. What this means is that you should expect to match your odo up whenever you see a mileage marker, no matter how correct your odo is, the mileage markers take precedent. An odo that adjusts up and down in tenths is important.
Hope that helps with a bit of local knowledge. Check out the offroad section in BARF, too, more locals active there.