Everything has to be reengineered. It's not just an engine swap. It's an engine, transmission, cooling, exhaust suspension swap. If you do go ahead, I would recommend aluminum heads to reduce weight. Finding a suitable adapter plate will be a challenge, and the engine mounts have to be changed too.
1966 109 5 door wagon 300Tdi "spermaceti fueled"
1994 RRC LeWiB "ruining the air behind me"
All my troubles are Rover