If it has an alloy head it will be from a P4. If you post the engine number I can probably look it up for you . Good practise is to torque it down in increments, say three runs round . increasing each time.
If you join the LR Series one club forum , members there will have done this before . It was a common upgrade for competition motors. The alloy head with an SU carb breathes a lot better at the top end . My first land rover was a 1949 model and it had a 1955 Rover P4 60 engine in it which totally confused me. Back in the 1960's there was no internet & I ended writing to Rover to ask what it was . I still have the letter I got back explaining things.