>>Thanks. Do you have an actual mekor (perhaps in the back of your kitzur) or just a footnote? <<
That was the mekor the (Darchei HaHalacha: al pi Maran Ha Shulchan Aruch, Ben Ish Chai, and the Kaf HaChaim). I will try to continue looking for more sources.
>>I just heard recently that the shulchan aruch; mishnah berurah writes that one should be dressed in Shabbosdik clothing on Purim. Could someone please confirm? <<
Confirmed. (Though I have heard that either a costume or bigdei shabbos are appropriate)