The transmission would be my only concern. The older transmissions aren't as durable as the late '80's early '90's, but it wouldn't be enough of a concern to pass on the truck. You can get the later model transmissions for under $200, and depending on its mileage, it may no longer have the original transmission. If you aren't aware of the procedure to test the transmission w/o road noise, you can shift the transfer case into neutral, and with the engine running shift through through the gears as if you were driving the truck. The '84-'85 X-cab are one of the favored year Toyota's to build, you get the extra room of the X-cab and they are the only 2nd gens to have a straight axle. A set of dual cases(21 spline) will bolt right up, and rather than doing an SAS you only have to replace the weak links in the SA, i.e, birfield joint, knuckle studs, push pull steering, etc. and a lot cheaper in the long run to build one over the 3.0 Runner.
From what I understand the HG issue was originally caused by the ban here in the U.S. of using asbestos in the gaskets, and Toyota didn't account for it. The 7m engines suffered from the same problem, a higher torque value resolved their issue. TTY bolts were used on the 3.0 due to the design of the intake. Where you normally go back in and re-torque head bolts after a few warm-up cool down cycles, having to remove the intake system makes it a longer job. Many owners of the 3.0 have been able to put 2-300k on their engines w/o the HG failing.
The only other issue I didn't mention w/the Runner is recall for the steering relay rod which is applicable to all the 3rd gen rigs('89-95 non-Tacoma) and all 2nd gen Runners('90-'95). The rods are cast and they have been prone to break at the pitman arm. The recall started in late '05 or early '06 and is still in effect as far as I know. I was fortunate with mine, it had apparently cracked(you can see the age patterns in the pic) long before it finally broke. When it broke I had just as entered the trail, anywhere else along the way and the truck would have likely been been totaled.
Give Toyota a call to see if the steering relay rod recall has been done on the Runner, it wont cost you anything to have it done, and normally takes about 3hrs.
