carbed out

Honestly, I'm going to go down this road.

The intake you have is really probably pretty wrong for this combo. It has the big ports for a 340/360 intake when you have a small port 273. Probably loosing vacuum signal to the carb pretty badly. Something like the edelbrock performer is probably better for this combo.

The next thing is the 670 carb is going to always be too big. Your original Edelbrock 1400 may have been okay other than the economy calibration. I'm not sure if you tried stronger step up springs to make the metering rods change states from economy to power faster or not, but that would help a lot if you haven't. I wouldn't run a carb bigger than a 600 on that engine. You're probably going to want something like the 570 avenger as opposed to the 670.

I agree you should try more initial timing. Get the vacuum gauge on there and try to find the timing with the highest vaccum. My 340 has about the same amount of idle vacuum you do and I run 22 up front, which is what it likes.