The Drag kit and your custom kit will probably be completely UN-interchangeable.

Meaning you will need a new downpipe, partially new piping (especially if running a DSM SMIC)...you would need the whole drag kit as if that custom kit was never on your car.

I wouldnt waste my time personally. Youre going to need some sort of fuel management too...why go through the hassle of getting this setup running right only to have a completely different one in the near future.

If you want to stick with this kit, make good power with it and keep it that way, I would go for it. Find out the EXACT componenets of the kit, and we'll tell you what else you need to get it right.

Also Im assuming it isnt a straight T4, he probably means T3, judging by the sound of the kit.

Youve got a lot to find out. You say its run at "stock" boost levels. Well that depends on what turbo this is and what the wastegates "stock" boost is. 7, 11, 14...who knows. Depends on what we're dealing with here.