Yeah, I have one in my Supra! It is a great motor that is not too heavy, I can pick up the short block myself and put it in the bed of a truck. Very easy to work on (with almost no special tools needed) and very reliable as long as you use ARP studs and prep the block and head nice for the headgasket. You can get a low mileage longblock for around $600 and with a $450 turbo upgrade, 3" exhaust, and a boost controller it will make around 275hp and 275ft/lbs+. Throw in 550cc injectors and a AFC and you are looking at 400hp and 400ft/lbs+. Check out socalsupras.com and supraforums.com for lots of info. Or email me with questions.
Still a great motor but hard to get substantially more power out of it. The stock numbers are still respectable at around 230hp and similar torque number. The turbo 7mgte is not really harder to work on and only about a hundred dollars more when purchased used. The only thing extra to deal with on the turbo motor is the intercooler and its piping. I think that a n/a motor with a turbo running low boost (6-7psi?)would be kick ass for off-road but would take a lot of time and tuning to set up properly.
I dont know I would be concerned about dirt in the turbo, extra stuff to go wrong like heat leading to detonation, etc... Plus like you mentioned harder to get it to work right in the car.
if you could get a n/a motor to+250 hp that should be enough for a buggy in the dirt.