This is the view inside of the ceiling with the new wire pulled in through the hole in the laminated beam.

The hole for the octagonal electrical box that will support the light fixture. The existing cables in the ceiling are set back far enough to provide clearance for the new box. You can see the side of the laminated beam on the bottom edge of the hole.

A 4-Inch diameter by 2-1/8-Inch depth octagonal box was used here to give better leverage support as the box was mounted on the side using #10 x 1-1/2" sheet metal screws and one fender washer where the knock out was. The fender washer allows for a little adjustment to get the box positioned correctly. The other screws lock it in place. Note the copper ground wire attached with a 10/32 screw.
The wires are tucked up inside of the deep octagon electrical box. This is another good reason to use a deep box, there's more room for the excess wires.