Apologies for not commenting on this thread sooner, I dont seem to get on here as much anymore.
The LJ70 your looking at looks great!
They are awesome trucks and will go forever if you keep the rust away. Look for rust at the bottom of the B pillars when you open the driver and passenger door. Along the bottoms of all the doors. Below the windscreen and around all wheel arches.
Before starting the engine check under the bonnet to make sure the engine is cold, Check the oil and unscrew the oil cap and look inside the cap for any signs of
mayonaise which could indicate a blown head gasket/cracked head. Then when it is started check to see what the smoke looks like on start up and how easily it starts.
Check underneath for any signs of oil/fluid leaks.
Check all switches/electrics are working correctly including electric windows, central locking, lights, horn etc. Check what condition the upholstery is in, in particular the head lining as they tend to sag on most 70s'.
Finding minor issues might help you haggle the price down a bit.
Good luck.