Start with elring gaskets if you can get them. Some of the best in the business. Be very meticulous on reassembly. "You only have one job". You only have one chance. There WILL be more parts needed than you think. Some will break (small bits) from age. Replace anything that is suspicious or will require the heads or intake to be removed, to replace later. With the labor and $ required, plan on keeping the truck for a while.Replace all cooling hoses that you haven't already. One blown hose and you could risk overheating the motor, and will be in the same situation your in now. Once you have decided to do the HG, your in it to the end financially. It would be costly to turn back in the middle. You will have the piece of mind with a reliable motor. Can't remember if Land Rover had cured timing tensioner issue for MY 12. If not, you have lucked out at 138k, and should look into it while in there. Can't remember if front timing cover has to come off on the 5.0 for just the heads, if so the H balance wheel is a bitch without the tool. Torquing the heads WILL hurt the next day.Wrenchmonger would know. And please get the heads checked and cleaned up by a reputable shop.