FYI : when i went to 4 bolt driveshafts i used hr31 companion flanges, i was told by numerous sources that thats what you use, when i fitted the companion flange it would sit about 10mm outside of the a arms, it didnt seem right but i just assumed thats how it has to be, only by chance i discovered they where wrong! brae had is hr31 apart and had done z31 5 stud conversion, i borrowed a z31 companion flange just to compare out of curiosity and boom!....
z31 companion flanges are shorter so anyone wanting to put hr driveshafts in r30 u must run z31 flanges!