Web search indicates D700 is Part no.1878249. Ebay seller says D700 is for 53-64 and is GM part no.1878249. This seller says 1878209 and fits 40-54. BorgWarner website says 1878209 superseded by 1878249.
So seems to circle back.
kennethw is a member here that owns a generator rebuild co. Hasn't post in a few years. Try contacting. [email protected]
Hope he is OK, he is a good man. Free advise.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn