For an all original Z28, it is always better to keep/rebuild all components like water pumps. An early 69 model year pump like yours are more rare to find, so keep it!
There are some small rebuilders around that can rebuild and return your original pump. If you have a press, you can do it yourself, but you will need to practice on other pumps and make some special press blocks.
I have rebuilt my pumps using a kit from ebay (northwest supplier) which have worked well.
New pumps will not look the same as your original and have the part number 3953692. Almost everything has a part number and people will look for that to authenticate a Z. my .02