My mate has 1999 Defender the same has mine but he has Mud Rails fitted and the rear bulk head removed and it makes a big difference, feels a lot bigger and more spacious than mine. He's a big lad (tall and broad) and has no problems driving it.
I'm 5'10" and I had to put a smaller steering wheel in so I'd think it's a must for taller people, I also have aftermarket seats fitted which make a big difference. The great thing with a Defender is if something isn't how you want it you can just change it.
im 6ft 4 but i have fitted seats from a volvo with no rails on which sit lower and further back,it gives me room for when ive got my heels on or i just cant get my knees in..
I'm 6'4" (33" inside leg) and son 6'7" both fit ok in 300tdi 110. I find it a little cramped on RHS with door bit close but head and leg room fine. Could be different for you depending on leg / back length
The only real problem was that I couldn't use the intermittent windscreen wipe as my knees stopped me from pushing the stalk down but it works fine after I very carefully bent the stalk up with a pair of molegrips.