Spitfire King,
After intense research, and modeling many desert dios for the era you are asking about I would strongly advise that you look into purchasing 1/35th scale figures from DML (Dragon) their products are listed not only on the DML home website but many dealers as well. Also, Tamiya has several possible soldier ideas and one is that they have the Desert Rats in assorted gear. DML's figures are highly detailed with many extra add on features and weapons.
In the case of re-doing the figures you may find that if you mix and match body parts with other similar figures within the two manufacturers that I mentioned you can minimize "surgery" as the idea is to create an image to let the viewers see a certain action.
As far as the Matilda tank, Tamiya has a very good model and I would suggest that brand if you have not already made the purchase. I have the following on the crew (4) and tank specs:
Commander, Driver, Gunner, Loader. Considering it is a small tank there is not much room for more! And it was never gunned to take on the Afrika Korps for much longer than mid- 1941 when the German "88" appreared on the scene of battle. The model dipicts the Matilda armed with a 2 pounder main gun, this is not a very large bore size and is equal to only about 50mm if memory serves me right, I'm a Navy Gunner's Mate Chief Petty Officer so not much expertise in British gunnery! You can surmise that if the British 25 Pounder gun is equal to 88mm it would be close.
As part of your diorama which sounds great!, keep in mind that reference photos help and many are on-line within websites of folks who model everyday, simple to the most complex dioramas you can imagine, after 45 of my 56 years I decided to please myself with the amount of details and you would be surprised with how little in the way of detail you need to make the dio look really sharp! I model in HO scale RR and 1/35 armor and 1/48 WW 2 Navy Aircraft(mostly, some USAAF) so I relate one to the other when building up scenery as the method is the same.
My references to the Matilda are from:
Chamberland, P. & Ellis, C (2000) British and American tanks of world war two.pg.56
Cassel, London
The book is distributed in the U.S. by Sterling Publishing Company
387 Park Ave. South, New York, NY 10016-8810
The book last listed for $24.95
Best of luck and let me know as well as everyone else on this forum, we are all here to help!
johncpo