I have used 1/2" x 13 x 2" grade 8 bolts to replace messed up studs with no problems so far. I just used regular bolts, washers & nuts, nothing serrated or flanged.
I was up there Easter weekend, and our group rode Frieling's property, I believe it is now being run by his granddaughter. Here is a link to their Facebook page: https://www.facebook.com/pages/Frielings-4x4-Park/161069060711826
It's a shame to hear about trails closing at Green Acres because...