I can only suggest the B&S engine overhaul model that covers engines of approximately that vintage:
http://www.tpub.com/content/recoveryvehicles/TM-5-4240-501-14P/css/TM-5-4240-501-14P_78.htm

I have not seen a better manual, though I think there are other manuals for the current engines. Use the "next" and "back" buttons to see other pages.