Hi Andy - I recommend you replace the brake shoes and ensure the brake components are thoroughly cleaned. I use a can of brake cleaner. Decontaminating the brake drums is a bit more involved though.
1. Ensure all rusty edges and rust flakes are removed - I use a small angle grinder to remove the out wear lip.
2. Clean the brake drum thoroughly with brake cleaner.
3.. Set the brake drum up on something non-flammable ( I use a brick or axle stand.)
3. With a gas blow lamp at a low setting I start to heat the drum form the outside - constantly moving the flame around.
5.. After a while you will start to see any moisture or absorbed brake fluid coming to the surface and a light film of rust forming on the surface - this can easily be romoved with emery when the drum has cooled.
6. Do not heat the drum from within as there is risk of damaging the wheel bearing.
7. Afetr all component shave been correctly assembled fit the brake drum and operate the handbrake a few times - this will help centralise the shoes.
8. Bleed both rear brakes - until no air or bubbles emerge.
9. Using a screwdriver turn the knurled nut adjuster up a few notches at a time - this will involve nunmerous attempts- until the drum can just be fitted.
As a matter of interest what part of Northern Ireland do you come from - I live in the south east of Belfast.