Kallax drawer insert - standalone brackets

I bought this Kallax drawer insert in order to put on a shelf that I have. Unfortunately, it only worked well with the precision of the Ikea Kallax.I first tried making a wood jig to hold the sides together. It proved to be not accurate enough. I've included two different iterations. My first was just one peg, the second added one to be able to grip the side. I would imagine this would work on all of the Kallax drawer inserts but have only tested with the one linked above.