i have a 2004 impala ss with supercharged 3.8 serise 2 haw do i identify the supercharger the vin is 2g1wp521148176388

They look a little bit different, this is a gen5


And this is a gen 3


One the gen 3 the throttle body mount is straight. On the gen 5 it'* off set a little bit. The bolt pattern is also different but that'* a bit harder to point out.

theres no markings?

Nope. If you can post a few pictures we should be able to tell for sure.

will i have a problem if i drop my pully down to3.4 with out doing anything else and how much boost will i gain

Yes, I don't suggest going smaller then a 3.5" on any engine without supporting mods like exhaust and rockers.