is a OVERALL 28" glasspack too big? Adn since I have 2.5" exhaust piping...do I have to stay with 2.5 in/out? as there is more of a selection for say 2.25 in/out (selection, meaning length)

Thanks

 

You need to match the glasspack with the pipe. Putting smaller glasspack would create unblanaced air flow and it would be too restrictive. Personally, I would go with 21-23" (23" is one that I have). I think 28" is too long.