Can anybody help me out. I need to find out what centres fit a RN20 Hilux housing, eg; what year/model hilux do they come from? and what ratio's do these come in. I have heard that all Hilux centres fit all Hilux housings but i find that hard to believe.

IIRC they are a 'G' series diff. should help with finding centers etc. (also MKIII supra's z20 soarer's and a couple of others have a G series diff-that does need a spacer - good option for LSD's)
also i do belive that the majority of hilux centers do fit, but some take a bit of spacing to get it right.

apart from the new ones they do pretty much all fit. my lsd in my rn20-25 housing is from a 92 hilux 2wd. just make sure you get a low pinion diff not a high pinion as it will through all ya geometry for ya driveline out.