I know that the HO's in '68 and '69 were sent to Hurst without an engine. The 455 were put in after the car left the plant. I'm not sure if they put in an engine with some type of stamp or not. I confirmed this with a local owner of a '68 yesterday. He knows quite a bit about the HO's and has three. He just purchased a '72 442 from me.
There is a nice 1970 W30 on ebay.
http://cgi.ebay.com/ebaymotors/ws/eB...66511&rd=1