The 1G B12 uses the same front brake lever, but the clutch lever is different since the B12 has a hydraulic clutch and the B6 is cable operated.
Katana 600's & 750's use the same levers as the 1G B6 though.
For exact years, check one of the on-line parts catalogs, like
this one.A B6 requires a slip-on with a midpipe, or surgery to the stock exhaust. 2003 and earlier B12's can use a bolt-on can or a slip-on with a midpipe. 2000-earlier B12's have different clocking of the muffler flange than the 2001-2003 models, so a bolt-on can would be different for a 1G than a 2G.
A slip-on with midpipe from a B12 will work on a B6. You could use a bolt-on can for a B12 on a B6, but it would require the correct OEM B12 midpipe.