Could you clarify what you mean by "Falcon 20 D (Long range)" which I'm not sure exists?
The D, E and F basic models powered by CF700 were, as far as I remember, around 1630nm give or take a bit I'm not a pilot so the figure are just from memory. The F model having a little bit of extra fuel in the tips (and full span leading edge slats).
The long range came when they re-engined some with TFE731's which pushed the range up to around 2250nm. I surveyed some re-engined ones a few years ago and very nice they were. Maintenance tends to be quite labour intensive!
Mike Echo