5/16" Rods for X-Axis to Drilling Best Practices

The parts I ordered from Spain for a Prusa i3 seemed to fit together pretty well for the base using the 5/16" smooth rods for the y-axis; now I'm on to the x-axis and the parts I have have alot of places that need to be drilled such as the left and right quarter ovals below:






So what is the best way to go about this? Where do I put the drill tip for best results, and should I use a 5/16" drill bit for this, or something a bit smaller?

I bought a Drill Guide to make sure the holes are drilled straight, but I'm still a little nervious about doing it, so I'm here to ask about some best practices for this.

Thank you,
leeand00

Those look like support towers for printing. You should be able to break them out easily with a screw driver.

Don't remove the horizontal pieces!

Just a note. My printed parts were so terrible that I had to redesign and print new ones. If you are interested you may want to look into these replacements. They add about a 1/2" of build height and move things forward abit so the extruder doesn't bump into the idler. Also I set them up to use set screws to fasten the x rods. No hammering to assemble and align. [www.thingiverse.com]