I did a 24 hour race, or at least I should say, I started a 24 hour race in Ringwood. We missed the cutoff time for a checkpoint about 13 hrs into it (we were over 75% finished mileage wise) and I did the EMS Sprint Race in Harriman earlier this year.
If you can't navigate, these races are brutal, frustrating and way longer than they need to be. However, the sprint races are really good, in that the courses are smaller so the teams bunch up and you can almost play follow the leader for most of it and there generally isn't an orienteering leg (which the longer races usually have) which saves alot of time.
The navigation in Ringwood isn't that bad, there are well marked trails and in the EMS series you can use your own maps, and there are plenty of good trail maps available for that area. You could probably do the whole race and stay primarily on trails. The mountain biking ranges from technical single track to firebreaks and wide trails.
Physically you should have no problems given the times you can do, I've finished about 4 or 5 of the sprint series races and I'm nowhere near a 4 hour marathon. They are a blast, fun wise, you can't get any outside help, but teams can help one another on the course, in every race I've done, I've always helped and been helped by a wide variety of characters.