Hello Darren, welcome to pensioners anonymous.

You can tell the difference between a Mk1 and 2 by the rear of the car from the windscreen back.
The Mark1 has the panels behind the windscreen the same height as the front wings.
The Mk2 has an additional strip screwed to the top of the panels from the windscreen back making the rear panels higher than the front wings.
Certainly the fixed font axle will be a problem on surfaces that have bumps in them such as your average field. The solutions are fairly simple if you are a DIY man. The wheel lifting off the ground and losing drive can be improved by remembering the three legged stool principle where you only have three points of load contact between the body and the ground.
This is achieved by pivoting the front axle in the middle so the body has three points of contact, two rear wheels and the central pivot of the front axle around which the two front wheels can oscillate. There are drawings available from Richard for this.
If you look under any version of Land Rover, you will see that principal being used to make it the best 4X4 by far as they say.
Hope that helps.
Regards,
Brian.