I dealt with things of this nature back in my dealership days but back then at least they would send us the tooling we needed when they changed something upThose guides can be kind of generic. Length, inner, outer diameter can be massaged to serve in various cylinder heads. Engineers through the years saw reason to increase valve stem sizes due to different materials used.
O.D. of the guide is increased in some cases to compensate for their bore in the cylinder head needing enlarged and trued because of a guide coming loose and beating it's hole o/s and out of round.