5.9L Magnum questions

KB 107 will bump the compression up, but then you have the expense of balancing the bottom end.

Agreed, I think for the OP's goals and since the short block is already in good shape it's not worth the expense of swapping pistons and rebalancing everything. 9:1 isn't excellent but it's better than the 8:1 (or less) of stock LA 360's and still allows you to run regular gas which saves quite a bit on fuel these days.