Anyone knows if the meter bracket from a 2004 GS500F will fit a 1991 GS500? It looks physically similar...

I strongly suspect it would. You can always check the parts numbers using the online microfiche - if the numbers are identical, the parts are identical.

If you need a bracket, I have one with some very light rust/rash.

I have an 04 bracket holding my 89 gauges.The F model and some late E models got the charcoal colored brackets.Pre 01 got the silver.There should be no fitment issues.