Will 2005 GS-500 carburetors bolt right onto a 1994 GS-500? 

And if so;  with the cables all fit the same?

And if so;  will the bike run OK with the newer carbs fitted?

Your 94 carbs are easier to trouble shoot dude ... I'll very much fix any damn thing worng with it for $45 + whatever is wrong ... and i have a good set of carb parts I can sell you if you got bad for $5 each or less ...
05 carbs will bolt on, but they need the 05 switch assy cos they have different cables ... dunno if 94 cables will fit it ... then they still need to be jetted and fiddled right ... not worth it.
However in the future the 04+ carbs are gonna get cheaper and cheaper ... due to supply getting well expanded ... so we may have a point in going to the newer type ...
I like the old type just fine though ... fix it, dont just randomly swap stuff ...
Cool.
Buddha.

I wish my 04 didnt have the tree system, they are a pain in the ass to jet and diagnose Id rather have you main and pilot and thats it much easier to figure out.

Mach1 - I am working on the theory that ... you ignore the mids and diagnose and work the other 3 like an older carb ... but older ones are still cleaner I would think.
Cool.
Buddha.