Hey there, another sparky! I used 3" EMT for the muffler delete pipe on my truck, perfect fit for the stock exhaust system. However, the intake side of things, for the DIY filter, any parts store can cross the number to what ever filter brand they have. As for the pipe needed, if you have the late '99-'03 7.3 PSD, you only need 3" of 4" exhaust pipe. A local muffler shop sold me 3" for the same price they sell it for by the foot, a hose clamp from the hardware store, and a few minutes to pull out the old air box, and in 15 minutes, I was done.
So, to answer your question, no, 4" EMT will not work, too large outside diam.
Good luck!