5.9 Magnum exhaust/intake combo help

Well, there's basically 3 intakes for the Magnum. M1 dual plane, RPM (& the knock off's) & the M1 single. If your cam upgrade doesn't warrant the RPM, then the M1 dual will do. A 600 cfm is excellent for street duty. While many will argue for more.....
If you can look for the early magnum exhaust manifolds, do so since they have (IIRC) 2-1/4 exhaust ports. For a melo cammed 360 & dual plane, 2-1/4 dual exhaust will work just fine. Just make it efficient.