In a nutshell, spider gears are what allow the two rear axle shafts to turn at different rates of speed making cornering a more pleasant experience on road and the transfer of power to the wheel with less resistance off road (bad thing). Welding the spiders ensures that both shafts and wheels/tires turn at the same rate (poor man's locker a.k.a. a Lincoln Locker named after that brand of welder). I'm sure www.howstuffworks.com can explain spider gears better than I can

At any rate, so long as the R&P hold up, and the axle shafts, and the front end hold up, and Dave/Robert take it easy it should limp along just fine. Last I saw on the tracker, Rod Hall was ~50ish miles into his second lap just past pit 2...but maybe I mis-read the map.

Goodluck, Dave!

P.S. Patrick, I posted this from my phone, have you been keeping up with XOC via your new Verizon toy?