As Jason, the originator of this cocktail, says, "A scotch with some backbone, such as Johnnie Walker Black, is required to stand up to the arrack." That...
I'm not sure this is a good use of arrack - I used By the Dutch batavia arrack, and most of the complexity coming from the mash bill of sugarcane, date palm and rice was lost in this drink. It's also quite dry with such a small amount of benedictine. I would recommend just making an arrack old fashioned if you want to put the spirit to good use.