Hello Alan and "WELCOME ABOARD !! "
I know the Shepherd boats well but not the details. Most are still in Canada, coveted all over the Muskoka Lake region, but a few have made it to the states. If your boat has the "powernaut" system Eaton provided back when Chris Craft was acquired by NAFI (1962) then that sure validates the year of the boat, etc. Many companies were using Eaton power systems. If you have one of the 215 Buick jobs, it is a rare one indeed, and well worthy of restoration and the boat show circuit. We have a bit of a following here and a great appreciation for the older Eaton systems. Good luck with your search for more info, we'll help if and when we can. In the interim, please start a fresh thread and send us a photo or three of your Shepherd.
Here is some info http://www.network54.com/Forum/424840/thread/1340909614/Eaton+Powernaut