Need some advice on tuning my big block...

I don't use vacuum to set timing - tho I know others do it that way and swear by it. A timing curve is a very individual thing which is why sometimes it's a trial and error process and why some people think a car runs great when there's more room for imrpovement. A very basic setup - something of a starting point for an average sized cam, stock long block - would be 12-15° intial timing and a total around 38° with factory iron heads. It should be "all in" by 2500rpm, and the vacuum advance should be connected to a ported vacuum source. Even to reach that, depending on your ignition system, may require some extra work on your part.