SBC Tuning help needed

[808_67C10]

I have an older Mexican GM Crate 350 (dipstick hole on both sides). It is pretty basic - not a high HP motor. It has a edelbrock intake, Holley 670 carb with a 1" spacer and headers. It also has an electronic distributor.. that should be enough to help you help me.

I got the truck with the motor in it and when I pulled the valve covers, the valve train is super clean --- dont know how many miles are on it.

When I got it, I changed the plugs, wires, cap, rotor and I have never had good luck with edelbrocks and put a new holley 67 street avenger.

I found top dead center by pulling #1 plug and it is straight up on the balancer. There is a timing mark dohickey but it is off the the right of straight up like all other SBCs I have had. If I time it off the timing gauge on there, there motor is barely running and sounds awful... but, I turn it up to the mark on the balancer at straight up and she starts and runs but, it doesn't sound right. Then, I drive it and its ok till I get on it just doesnt feel right. I cant advance the timing 12 deg past the straight up because the idle will be too high n I cant bring it down with the carb. should I with this set up?

as for the carb, Its about 1.25 turns out on both air/fuel screws with 20lb on the vacuum guage (front vacuum port).

What am I doing wrong? Is there something else I can try?