tein springs installed with stock shocks....how does it handle after this install?

also, i got a DC JDM 4-1 header, my choices are...
1) wield it on current cat (i'm thinking this way cat will reduce the airflow)
2) custom a test pipe (hassle, i have O2 sensor and greddy a/f sensor currently)
3) try to find a cat that fits.... anyone knows where i can find this? something about 2.7" i think...

any suggestions would be nice...thx.

 

If you weld the cat to the header something will break.