Yep, sounds like you got it. The orifice you need to drill out is the brass piece that connects your gas line to the burner. Looks like this-
Here's a pic that shows the hole size difference between high pressure LP (left) and NG/low pressure (right)-
FWIW, 1/8" is kind of an average, and depending on your exact gas pressure you may find that you need a slightly different size orifice for optimal performance. Start small and work your way up, since it's much easier to enlarge the hole than it is to shrink it. I started with a wire size 35 drill bit, and ended up working my way up to a size 29, which is a couple steps larger than 1/8".
Also, depending on where you live the shipped price from agrisupply may not be the best. They have pretty high shipping charges to the west coast, and total shipped price here in AZ was actually cheaper through Amazon.