I don't know off hand what neck the PGM90th has, but the 100's is an original wizard..
If your RG450 has the all-
access neck joint, the PGM100's neck will have to be modified to fit your guitar.. It has the old
neck joint with the fingerboard extention.. I think someone on here has done this (made an old joint neck fit an AANJ body).. Probably not an easy thing to do though...