Step 1: Locate peg holes
These chucks have a 1/2 - 20 mount thread, I had a 7/16 wood dowel from another project for this lathe, which fit perfectly through the center hole. I got a scrap piece of MDF, using a combination square, I found the length wise center and made a line. Where I decided to place the pegs for the chucks, I used the combination square to draw a line perpendicular to the length line.
Then, I placed the MDF into my drill vise, centered over the crossed lines and drilled.
Note: I know the distance between the first and second peg from left is off. I accidentally put the three jaw chuck next, instead of the second jacobs chuck, when I measured for the second peg, so pay attention when you're doing this.