My own memory of Gan is that the runway was about 7000ft long, and it certainly fitted within the physical boundaries of the island! The relatively short runway was a bit limiting for many of the types that staged through in the 1970s, prior to its closure in 1976.
As for Elvington, I don't have an RAF BINA from before it closed (93), which would show the accurate ASDA - i.e. the length of concrete including stopways - but the documentation I do have shows 9800ft. While some may measure runways in statute miles, the RAF never has. I did much of my own early Jet Provost T3A flying from Elvington. The facilities there at the time were extremely sparse!