Any Land Rover is more than capable of tackling most greenlanes without any modifications, even the Freelander. 90/110 Defenders are the easiest to swap between hard and soft top but still not a 5 minute job! And yes a snorkel will be available to fit any Land Rover engine, if not - it's not a difficult job to 'bodge' one yourself.
Standard in the right hands is more than enough to scare most people.Most green lanes are well within limits tho a plan B like a winch or a companion with a towrope is alway sensible.When your adrenal glands are exhausted you may need to modify!!