Get the fittings for '70 up big block motors. Herbs, Mega, etc. all carry them.
The 1/2" fitting has a 1/4 pipe thread so you'll need to use a pipe bushing from that size up to the thead in the water pump housing. IIRC it's 3/8 pipe thread. Home Depot sells them in brass. I got my nipples from Herbs.
http://www.herbsparts.com/proddetail.asp?prod=HNK-2The longer 5/8" fitting goes in the lower empty hole in your pic. The short 1/2" fitting goes in the hole up top where you have an old 5/8" fitting.
