Is that a T or a GT with the PEI ignition? USD's on the front of a T500 seem like overkill but they are short enough to fit nicely. For the rear swing-arm, look at the GS500 for a narrow mono-shock rear end or possibly a dirt bike like the DR350. If you want to keep the twin shocks, the 94-03 CB500 swing-arm looks narrow and beefy but it looks asymmetrical so fitting shocks might be a challenge.
There's a bunch of modified T500 pictures here to give you an idea of what's possible:
and there is a scan of the factory manual posted here:
There's a few specialists for the T500 on your side of the pond as well: