Parts diagram for the T500 steering damper:

Turns out the spacing between the T500 damper bolt (part #11) & the triple tree stem is about the same as the spacing between a GT500 fork lock bolt & the triple tree stem.
Bottom of the T500 triple tree:


Bottom of the GT500 triple tree:

Bottom of the GT500 triple tree with an M6 socket head bolt + spacer + nut:

Bottom of the GT500 triple tree with the T500 upper damper plate (part #6):

Bottom of the GT500 triple tree with the T500 damper.

The upper damper plate (part #6) & damper hub (part #8) will need some work. Some of the plate will need cut off so that the forks can move from lock to lock. Some of the hub OD will need filed down so that it will fit inside of the stem.
This leaves the question: would a high strength M6 socket head bolt be strong enough? (The treads on the T500 damper bolt (part #11) are bigger than M6.)