Just as an idea to make it really personalised, hop onto the National Archives and see if you can find your uncles service records. Now there's no guarantee that those years records will have been released yet, military confidentiality and all, but if they are released they should list not only his years of service, but which squadron he was attached to. Find out that, and not only can you paint the Harrier up to the same squadron markings, but you'll probably be able to find out from Squadron records, which I gather will be easier to access, which variant of Harrier he was working on, making it even more personalised. If it's 1:72 scale your going for, then Airfix, Revell or possibly Taimya will probably be your go-to brands I'm guessing.
Oh and I'll vouch for Osprey books - I've got one on the Napoleonic Wars, and I've read quite a few others and not only are they meticulously accurate, but they're full colour and at approx £10-£20 they are worth every penny for what you get.
Just a thought, but get him to regale some of his stories and possibly build the diorama around a particular memory he likes or finds funny etc.
Hope this helps, Good Luck!
EDIT! - Just looked in your gallery - As a self-confessed Napoleonic aficionado, I absolutely LOVE those Highland Guard, especially the feathered bonnet - Epic! I'm hoping, when I get some funds together, to do a Napoleonic themed
IG army with all the trappings of the Peninsular War era British Army - Belgic Shakos, crossbelts and lots of red!

Unfortunately, Salamanders are taking up all my funds at the moment :(