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Great. You know what's next.
Time for pic's.

+2
You mentioned a little worry about not wanting to weaken the old wood. This would be the best, cheapest, and strongest option.
You could also use old planks with a little story behind them for...

Look for porch swing hanging kit or you could use a lag bolt extended from both sides of the 2x6. Just be sure to cover the lag bolt to not ruin your suspension. The lag bolt can be used like a large...