Thanks for posting and welcome
This is an oddity. One sees tableware, as in a carafe or decanter, which have an insert meant to contain ice to cool the surrounding liquid. I believe this is different - my hunch is that one part was for the alcohol and the other for the mixer.
And yes, the FEDERAL LAW embossing is there specifically because federal law required this marking for hard liquor. I have a page on my website that discusses this.
The key to identifying the company behind this product is the "D-60" I have been building a list for years of these Distiller numbers based on labeled and otherwise identified examples. Most I find just by searching FEDERAL LAW bottles on eBay. Sorry, I have not pinned down D-60 yet. If you do, let me know!