sounds like that will be interesting rig in itself.I'm not sure that any Tundras race to be honest. They are pretty wide and long to fit through the Hammers. Short wheelbase, solid axle Jeeps have been the most successful in 4600 (the Currie Enterprises/Savvy team in particular) and Matt Pedersen won in the past in a V8 Grand Cherokee WJ. For Toyotas, there are some first gen 4Runners and older solid axle pickups that race and have done well.
I am navigating in 4600 this year in a Roxor with portal axles. We'll see how that goes!
Most pickups have too much rear overhang to navigate those trails in stockish form. More than likely you would be dragging scrap metal after the first obstacle. Look into the k.o.h. everyman challenge. More of a run what you brung class.
Thanks. Wasn't sure of the classes for koh.