There's a little more to setting up timing tables than looking at knock counts. If the knock counts are rising during a given engine operation you may have too much timing in that area. However, knock counts do not necessarily mean you have too much timing. Several of us have encountered "false knock" with these TBI trucks and have disabled knock retard altogether.
Vortec heads require more timing than the TBI swirlports. I've attached a screenshot of a modified vortec timing table in a TBI truck I've had good luck with. It should be a good starting point for you. This particular engine is 10:1 and tickled the knock sensor at 1200-1600 rpm above about 60 kpa. Your engine might tolerate a little more timing in that area. Copy the same values into the idle spark table.
Zero out your PE spark as shown in the screenshot and if your marine intake deleted EGR, disable the EGR as shown too.
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