What timing do you like to use on a stock base 455 ('72)? Spec is 4. I was running it around 12+ previously (mainly to try to somewhat compensate for the really slack timing chain). I set it at 8 with the new chain (stock set).
I haven't seen a Buick V8 that didn't like 12 initial. You might have to shorten the mechanical advance to keep from overadvancing at high RPM. Get the springs that come in the Crane adjustable vacuum advance kit. That way you can get all the mechanical in below 2500 RPM. Then you use the adjustable vacuum advance, limit it to 8-10*, run it off manifold vacuum, and crank the diaphram spring tension up until you don't get any part throttle ping. You won't believe the throttle resonse and low end power increase you get.
Everything is in the kit. 3 sets of springs. you can get all the advance in as early as 1600, and as late as 2800, and in between, by mixing and matching the springs. The adjustable vacuum advance rate is adjustable with a supplied allen wrench, and there is a cam to adjust the amount in degrees. The Crane instructions describe how to use the cam to limit the degrees. There is a much better way to use it. The ignitionman suggested the better way. If you get the kit, I'll post the pictures showing the difference. You may also need to put a bigger advance stop bushing into the distributor to limit the maximum mechanical advance. The Mr. Gasket advance kit comes with a nice brass one.
