The factory 340 intake isn't too bad, large ports no really big negatives until you get in to the EGR years. Its too bad the factory did not offer a dual carb option, yes they did have the 6 bbl but it doesn't clear without a hood scope in most car.
If you got the time and money Edelbrock RPM intake is a very nice intake and don't rule out the old single plane Holley Street Dominator which offers a very low profile and great low--mid range power with its small intake ports...I still swear the Holley intake pulled better than the RPM after 5,500 when I did the swap. The RPM was better taking off from a stop.
I'm running the old Edlebrock dual carb intake on my 340, love it and would not change it ever unless I went with the W2 heads, I got an old water heated Holley W2 intake sitting in my basement if I ever get my hands on some good W2 heads--or if China finally starts making and selling them cheap one day