Thinking of installing Texas Speed Rumbler 3" Cat back with Dynomax direct-fit converter on a stock 89 IROC with a 350 TPI. All I have are K&N air filters with air foil. How aggressive of a sound am I looking at? Any performance gains? How difficult will installation be? Thank you.

I would suggest looking for a different catback unless you absolutely love the sound from that one. All the clips of it that I have heard have sounded like crap IMO.

Install shouldn't be too hard if you are mechanically inclined. As for performance gain, I went from stock piping with a flowmaster 80 series to a 3 inch catback with cutout and never noticed a difference. Just better sound.