Here is another one from Tosh's castle tunebook. The harmony part is by Georgia Nettleton A cursory online search shows no actual castle with this name. Costello seems to be more of a title than a place.
Interesting recording. I like it with the harmony part. And thanks for the hint to Georgia Nettleton.
Nice playing together of the two mandolins!
This is very nice with the harmony. You and Georgia Nettleton do well together.