i have had 2 hard body trucks
one was an 86.5
the other a 90
the 86.5 had the Z24 motor in it, although a great motor was completely gutless.
i would go with the newer KA motor if you choose a 4 cyl.
the 90 was a fully loaded SE truck
I really miss it and it had 300k on the original motor.
as said keep an eye on the rear frame rail just above the rear tire for rust. that is why i got rid of this one.
deff look for the LSD option the V6 is also a very reliable motor and can run much longer than the KA, a timing chain is pretty costly to repair and that is a common problem in the KA's the V6 has a belt and is just as simple to change as any subie is.
as far as reliability these trucks are rediciliously reliable. i was a service manager at nissan for 2 years and these trucks had very few problems outside of normal maintance.