legal yes, possible no.... 
the range rover has the same chassis (except for lwb models) from 1970 to 1994 u can not use a 1995 body (p38 model) onwards on older models chassis. although, u can use a 90's discovery body on em. but frankly speaking, i'd prefer a range rover classic any day over a discovery!!!
and where defender (~1998-2007) and range rover (pre 1995) are concerned, they share mechanical parts. i.e engine, gearbox, brakes, suspensions etc.... but their chaises are completely different!!
why dont u tell me the exact model of ur vehicle and condition/problems n i'll let u know the best solution for it!! 
