If the budget will stretch that far, get one that has been rebuilt onto a new chassis in the last few years, if not then have a particularly close look at all chassis outriggers, rear cross member and front dumb irons, if they look good, then check all of the rest of it. I don't think the bulkhead is as important as the chassis, but it can take many hours to repair a rotten one, so check the footwells, door pillars and around the top front door hinges, and look for signs of rot under the windscreen. Swivel housings on the front axle are time consuming and expensive to replace - so check for oil leaks and severe pitting. If there are gearbox problems then bear in mind that it's time consuming to get the gear box out as the floor and seat box need to be removed to first. Mechanical parts are cheap and Land-Rovers are easy to work on so if the budget is tight go for one that does not need welding, but needs some mechanical work.