If your engine builder said use 28 degrees, that is what you should use. Modern engines / head / piston design requires less total ignition than the original 351c and you could be causing engine damage with less power. Scott Cook, the manufacturer of the heads I used, said start at 28 degrees total. After tuning on the dyno, the optimal setting for my engine was 30 degrees total timing.
FYI.. http://www.hotrod.com/articles...4rc-ignition-timing/
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