I would go ARB. I am installing mine as we speak. I have a AIM DC5000 Compressor, a 3 gallon tank welded under the bed, and air switches in the cab. I have not used it yet, but I will next week. I have a 98 NON-TRD as well. I hear the older NonTRD models like we have are more stout and strogner then the TRD axles. So there not too bad build up to what you want. Anyways, This is the route I am taking. If you have questions, just ask.
The problem with being locked all the time is you wear and tear on your tires are not that good cause your locked in. The ARB is either on or off, you can turn it off or on right there at a switch. Save my tires for the highway, no need to be locked. Now when my tires come off the ground or when I come up on some loose stuff going up hill, turn the locker on, and crawl.
But ARB will cost you. about 700 for the locker, 200 for the Compressor, 170 for air lines, fittings, switches, guages, air chuck ect. and about 50 bucks for a dryer/water seperator and oiler and filter. Plus 20 for wiring. Then 175 to get installed at a shop into your third. 250 if you take the whole truck in.
So I spent $1315.00. But The arb is lifetime i beleive, and I got on-board air, to fill my tires up at the end of the trail. I will also get CO2 tanks for backup if the compressor goes out on the trail. All i have to do is connect the line. Up to you how much you want to put into it.