What year is this chrysler small block HM318R36502350

Howdy
I am alittle confused about water pumps
What year is thsi block
chrysler small block HM318R36502350 ??
Can anyone help
I want to put a
http://www.flowkoolerwaterpumps.com...lymouth,-MOPAR<br>(1957-70)/product_info.html

Please help
I think its 68