I have a 56 Victoria, serial number would indicate a 312. I cannot get the idle to 400-500 and still have the car run decent. So, when the car runs correctly and I move the gear shift into reverse it slams. One mechanic suggested that I have the tranny looked at. A good shop said the tranny is fine, Just idles too fast. I have the PCV line reduced to 3/16 and venting into the air cleaner. I have Holley 4170---is  it too big. I have read some forum's that hint at that. Help=Please. Harold