I own an 89 Camaro, I am looking for a Y pipe 3" in/3" out.

for what exhaust? stock manifolds? i have one for the stock exhaust.

I plan on using aftermarket headers, shorty style. I already have a 3" cat and cat-back on there.

rich you need a 2 1/2 inlet

Yes with the headers I got from you today I need 2 1/2 inlets.

to bad we dont have a pipe bending machine