Welcome to the new Wizard Outboard Forum.
You are looking for this manual "Service Manual Mercury Outboards 1965 and Prior : C-90-25500" Shop around for the cheapest price.
The WH-6 is supposed to be similar to the Mercury Mark 6.
The PDF of the only free manual is available:
Go to: http://search.ebscohost.com/
Log in with:
User ID: marshall
password : public
-----Go under the Small Engine Repair Reference Center (look for the wrench), then Marine/Boat Motors....you will click on Mercury in the columns and then click on Mark 6 or Mark 6A.
Oops, I spoke too soon. A similar manual is available here:
Mercury Mark Manual can be found at:https://public-mercurymarine.sysonline.com/Default.aspx?sysname=NorthAmericacompany=GuestNA_KEY=NA_KEY_VALUElangIF=englangDB=eng
That is at: Mercury Marine - Parts and Catalogs - Outboards - K Series.