Not everything ever manufactured in the last 100 years is on the Internet.
The 763 number denotes a General Electric product that went into 1940's and later industrial
switching locomotives. Unless such a drawing has been scanned and posted
somewhere on the "web", you'll likely have to seek the data directly from a source
who still maintains or works on such equipment. Even then, it kind of falls into the crevice of
thrown out information. You know, the piles of manuals, spec sheets, and stuff no-one cares
about any more... thrown into the dumpster never to be seen again.
To illustrate, the attached photo is not of the 763, but is lifted directly from a maintenance manual of which one can be found at the URL listed below.
If you could find a manual for a GE locomotive with that particular 5GE763XX motor in it,
that may provide a drawing source. But even then, it may only be a drawing denoting
the apparatuses nomenclature as illustrated in the attachment.
Good luck,
John