Guys,refer page 15 of VMX magazine number 9 and the article on Galls 1981 OW51.
And I quote ....
"At the end of the highly successful 1981 season Steve put the OW(51) away in the corner of his workshop in Sydney.Its potent 498cc magnesium motor was removed and slipped into a production YZ250(J) frame,easily able to accomodate the OW motor because of its centre port/split frame configuration."
It could well be the real deal, albeit its not a works frame,merely the place it resided in 1982.