From what I gather the older cams were less concerned about emissions than their newer counter parts. In this theory if you put an older 1.6 hydro cam in a TDI it would be better than the AHU, AAZ cams. Mech and hydro had different opening and closing ramps and could cause chatter hurting the cam and valvetrain, but the mech cams would be better yet if that wasn't a problem.