is the power steering box from a 3rd generation fit to the 1st Generation? Also can I able to fit and use a 4th gen 1998 z28 rack and pinion and to replace my 1969 power steering box? Any painful modification?

The 3rd gen box is a common mod, and there are 14 pages of dicussion in this sticky from the brakes and suspension forum: http://www.camaros.net/forums/showthread.php?t=103139

There are several aftermarket rack kits for 1st gens, but I can't remember seeing anyone retrofit a 4th gen system.