My deepest condolences for your loss.
The main difference between those two years would be that a '58 would be a Land Rover series 1 and a '61 would be a Land Rover series 2.
one big visual difference between the two is that the doors on a series 1 are very distinctive, the glass starts higher up on the door.
The easiest way would be for you to verify the vehicles vin number on the title, with the vin on the the vehicle's body.
Theres some useful information on how to find the vin number here:
Wiki page on series Land Rovers:
If the problem that you're faced with is establishing the vehicles value, a heritage certificate from the British motor museum may help.