A Series Land Rover has good access around the radiator and comparatively few ancilliary items have to be removed in order to remove the radiator. Once the cooling system has been drained, it is just a case of unscrewing and removing the fan shroud, radiator overflow bottle (if fitted) and removing the top and bottom radiator hoses.
The radiator mounting bolts for any Series Land Rover are accessible behind the radiator grill, so the grill has to be removed. Once the bolts have been removed, the radiator can be lifted out - take care not to damage the radiator matrix on the fan blades as you lift it out.
Series Land Rovers can run hot if the radiator matrix is clogged up with debris or mud so use a high pressure hose to flush through it. Inside the matrix can also be flushed through and if a partial blockage in the core is suspected then the hose can be temporarily sealed onto the drain tap hole using whatever clips, tape, tubing etc. you have available and the radiator reverse flushed.
If the core is damaged and there is a leak, then you have the option of either trying to solder it, if there is sufficient access, or using a suitable epoxy based sealing compound on the outside. Either way the radiator surface must be completely dry for the repair to be effective.
There are still some radiator emergency sealants on the market which are thick and viscous and designed to be added to the cooling system whilst the engine is running. These heavy sealants should be avoided as they tend to partially block passageways in the engineblock and cylinderhead thus creating more overheating problems. Thinner, more modern, temporary sealants can be used but the best solution is to do a permanent repair.
Finally, now the hoses are off, give them a good inspection inside and out and repalce them if cracked on the outside or flaking is observed internally. New hose clips are best used unless the existing ones are not corroded at all.
It is also worth noting that if the radiator core did have sludge and corrosion deposits in it when flushed out, then the engine block will have the same, so if you can rig up your hosepipe to reverse flush through the block then it would be a job well done. A Series Land Rover usually has a very old engine block and few people bother to flush out the water channels in it. This could well be a major part of your overheating problem.