this is a little old but I have an nice set up in my 04 disco that uses an ARB compressor mounted in the location where rear air suspension compressor would have gone (inside a protective box) and then an old rr tank under the sill.
now that my mom has that rover for camping, I have set up an lr3 similarly but using an extra lr3 tank which is a stock part for the air supsension. that made fitting easy at least. we also did a cool custom fit for a huge Odyssey 2150 2nd battery.
updates will be on the lr3 postings.