Hello Mike
The condition of your brake cylinders is the result of water being absorbed by the brake fluid and the passage of time resulting in the condition that you find. The pistons in the cylinders are steel, the bodies are Aluminium and the result is corrosion when water is absorbed. If the bodies of the cylinders are in good order and you are going to rebuild them I would advise you to get them sleeved with a stainless steel liner.
You can get reproduction parts to get you up and going more quickly but be aware they do tend to leak, I am going through the same thing at the moment. I replaced the two rear cylinders in March this year, the previous ones only lasted 18 months before leaking.
I just discovered one replaced in March this year with about 400 miles on it leaking and fluid all over the back wheel. this is why I suggest getting them sleeved if you can. The master cylinder is cast iron I believe and can corrode for the same reason and can also be sleeved if it is in bad condition.
I replaced my master cylinder over ten years ago and is still in good order with no leaking, it just appears to be the cylinders that are a problem.
Let us know how you get on Mike and if we can help you out in any way. I am not sure about the Auto transmission , somebody else may chime in to help you out with that.
By the way Power Track in the UK stock parts for your braking system and know Allards , https// http://www.powertrackbrakes.co.uk
Good luck , Kind regards, Charles Gough