I used tapcon screws to fasten a pressure treated 2x4 to the blocks under the 4x6 timbers. The lighting was trenched out ahead of time and run in conduit under the center of each pillar. Then I would cut a small notch in the block with a diamond blade for the wire to run to the light. The light has a small plate made to fit between blocks etc. When running the low voltage landscape lighting wires though you have to run individual wires for each one and make sure each wire is the same size that runs back to the transformer. In other words the wire running from the transformer to the closest light needs to be as long as the cable running to the furthest light. If you don't do this the lights will be different brightness because they run off of DC power.

What did you use to drill the hole in the 4x8x16 block?