Not that difficult a job, fairly straightforward. Undo this bolt then the next fairly logical if you've got a basic undestanding of mechanical things and know how to use spanners.
See MBM Dec 2000, they did one there.
If badly scratched\corroded, not a bad idea to strip paint right off using stripper, and then have powder coated rather than repainting. Shouldn't cost more than about £40, you'll find a local firm in your yellow Pages who can do that, just make sure they only do the bits on the outside. One of my buddies had his done and left the anode on and they made a real good job of powder coating that too. Of course you've still got to antifoul it, but the powder coating's harder than any paint you'd use. Spares etc for Enfield outdrives are fairly easy to get and OK for prices (especially when comapred to VP). Try Keypart in Watford.
I did mine a few years ago, was easy. all, sorry all but 2 bearings are readily available,and seals, so you dont need to pay mega bucks for most bits, in the top is a 90 degree bevel gear, this is expensive if i remember, and its important cos another bearing uses a shoulder on this for its inner surface, apart from that you will be fine,
Check out Bob Knowles in Leicester for bits,he owns the rights to the manufacter of them so every one has to go to him for bits anyway,
PS Get a small manual just so you know how it goes back together LOL