I came across a copy of the old guide.grandtheftauto3.net on Archive.org and decided that when I have a bit of time I'll stick it up on GTA3.com. This time has come, and I've spent the last hour getting what was left of the GTA3 Core Missions Guide back online.
Naturally parts of the site have been lost through all these years, but minus the comments and print sections the site is mostly available for viewing. Enjoy.
GTA3 Core Mission Guide by P1agu3