HP2, back pressure is bad. A 2-1/2 inch exhaust will do you good.
3500 rpm for cruising? Damn, most any intake fits the bill except a tunnel ran and race single.
Use a dual plane. An inexpensive Eddie Performer will work great or even the factory intake! Which is no slouch.

When you talk t the cam grinder just tell him what your asking here and the cruise rpm of the car your cruising at. He will ask you a lot of question about your car and the intended purpose of it.