Fuller's brewery and Fuller's beers are close to my heart, having visited the brewery several times over the years, met with John Keeling, head brewer for many years and drunk copious amounts of their beer.
1st Question is that first recipe says to use flaked maize and second doesn´t, which one is better or who cares?
~ Fuller's used flaked maize/corn until John Keeling changed the beer recipes to all malt in the mid 1980's. (They use invert sugar in some high alcohol ales.) I would avoid maize.
2nd I can´t find Northdown hops here. Possible replacements have been mentioned Target or Challenger, but is it straight change or need to change quantities and which one would be better?
~ Northern Brewer at best being a parent of Northdown but Challenger would work also.
3rd Both yeasts(wyeast 1968 and WLP002) that are mentioned in recipe are almost impossible to find here for some reason, so now i´m trying to find replacement yeast. Have seen mentioned S-33 and S-04 from Fermentis and Windsor from Lallemand. Heritage English ale yeast from Pinnacle could also be one possibility.
~ WLP002/Wyeast1968 are clones of Fuller's yeast and have the marmalade flavour which defines Fullers's beers. They are, however, not good attenuators (63% - 70%) so you use more malt than other more efficient yeasts. S-04 is more efficient (74-82%) but may not have the marmalade trademark flavour.
If it helps, Wild About Hops in New Zealand sell a PDF book on British Ales with over 100 recipes, 4 of which are recipes for Fuller's ESB (cask, bottle, 1981 John Keeling tribute version with flaked maize and 2005 Anniversary version)