Small Block Chevy Question

[Bruce Edwards]

You can not install the balancer wrong. It may have slipped and that is why the timing is off with the light. If it has slipped replace the balancer. It is on it's way to a failure. It may also be the big problem with the engine. You will have a hard time setting the timing if it is moving around. Your parts changer should have noticed a bad balancer.
Did you ever get a vacuum gauge on the engine yet? You need to get some idea of what your base vacuum is.
Do yourself a favor and do not throw parts at the problem. Figure out what is wrong and fix that first. Then move forward with any other repairs you may wish to make. You may just make it harder to find the problem.
The high idle may be due to timing still. When you put it in drive the load slows the motor to a point were the vacuum drops off and the advance starts to fall off. As it does the idle comes down.
Again this may all still be tied to timing.
Look at the rubber insert in the balancer. If it is cracked and splitting out the sides you need to replace it NOW! You do not want it flying apart.