I have a Megan racing 370z y pipe. I want to put it on my 05 G35 coupe along with my isr single exit . Would the 370z y pipe fit in the car with stock cats? Or would I need test pipes?

Y-pipes are interchangeable between G35/350Z/370Z. The difference is the 370Z has longer dual pipe sections and a shorter single pipe section, overall length is the same though.