I think you are under estimating just how competitive rallycross racing is even at the amateur level. Even in an amateur event he would look rather silly bringing an S10 to a sport that is dominated by European automobiles.Ok so you do want an offroad/rally/daily driver thing then...I think you guys are taking it the wrong way, he cant afford a suby and he's not looking to build some kind of professional rally car anyway. So I would say look for a regular cab short bed, (you want as short of a wheel base as you can get) 4x4 preferably 4.3L V6 (you want as much torque as you can get to) matched with an auto with a small tight stall like under 3k so you can daily it with a really good tranny cooler and get some lower rearend gears if you cant find one with atleast 3.73 on it stock. just get a small suspension lift kit dont lift the body at all, you just want more suspension travel. get some good offroad wheels and tires, a bush guard with fender flares and go have fun.
You should explain to them what you have had to do with yours to run autoX...and you run on pavement only correct?yeah I don't think they also understand how incredibly poorly equipped an S10 is for autocross, the rear suspension on our trucks is probably the simplest and least effective design out there for automobiles, it's insanely cheap.
Not having an IRS your rear end is just going to hop everywhere and you'll go nowhere
driving trucks in the sand is an entirely different story