First of all, a few observations: A stock (or mild) cam 305 doesn't need an RPM, let alone an RPM air gap. You'll probably run into some problems getting it perfect with that intake. Secondly, 1500 RPM is WAAAY too much idle. That thing should idle at 400 all day. That engine is done by 5000, so idling it at 1500 is not logical. Of course, as others have pointed out, the carb is way too big which doesn't help.
It sounds like a classic mismatch of timing, idle mixture, and idle setting. First of all, for now, skip the jets and rods. They are strictly for throttles OTHER than idle. They won't change a thing at idle. It sounds to me like you have the idle mix too lean and have compensated by opening the throttles, then you set your timing. Here's what I suggest:
Set your idle screws to 1 turn out. Start and idle. Advance the timing... doesn't matter how much, just a good advance to make it idle. Back off the idle speed screw a bit, then re-advance. Its a common problem for newer tuners, especially with manifold vacuum on the ignition. What ends up happening is they set idle timing first. What needs to happen is tuning the carb first. Forget about advance at idle while tuning the carb. Throw a buttload of advance in, tune the carb, then back things off while adjusting the idle speed until you get to the proper 12* and the idle you need.