Don't know much about v8 engines but smoke, leaks and funny noises, the stuff you'd look for on any engine really. Structure wise you need to check for corrosion in all the usual places, ie have a good poke around the whole chassis with a screwdriver. Check the rear crossmember for rot, outriggers espescially the bulkhead ones, the bulkhead itself paying particular attention to the top corners, footwell area and the pillar where the door hinges are attached. If you get to drive it listen out for any clunking or banging or excessive transmission noise. A landy of that age could be a belter having had £000's lavished on it, or it could be a tired old dog that needs just about everything sorting, and as prices vary wildly it'll be up to you to decide.