Here's a write-up I found. http://www.landroversonly.com/forums/f40/power-steering-pump-conversion-52582/.
Unless you found a new one, it seems like these conversions are more aimed at D1's. If you read the whole thread it seems that it is more trouble than it's worth.
Where are you getting your ps pumps? My wife's D2 went 165k on a original pump before we sold it and my D2 is on it's original pump at 145k and still going strong. Unless your getting cheap re-mans from the usual places, longevity depends a lot on fluid changes/choices.
I would go OEM with a good warranty.