" The LWB ones have a greater offset (ie the rim sits out further from the hub face). might also be 1/2 in wider? A measurement from the rear face of the rim to the outside or inside edge of the rim will tell. "
does this sound right you land rover gurus ? I didnt think that there was a difference but am well prepared to be proven wrong and educated at the same time
Long wheel base rims tend to be slightly wider. about 6.0 inches against the short wheel base 5.5 inches. Later Defender ones are better again with 6 inch wide but with betetr off set. Then again go for a set of wolf rims which are 6.5 inches but mostly only found as heavy duty options on 130's and the miltary spec vehicles from which they got their name.
SWB rims are 5" wide, while LWB are 5.5". Defender (90 & 110) steel rims are also 5.5" & are actually the same as the Series LWB rims (post about 1968). A minor change of construction was made at one point from rivits to welds holding the centres to the rims. The Wolf or NATO rims are 6.5" wide as already mentioned.
There are heaps of 5" Series rims around, but not so many 5.5" rims. Not so few as to be classed as rare though as some people like to make out!
There are also a few other styles around (rostyle, Discovery, etc) depending on what you want.