Hiya Eric,
Well, this one seems to be a stumper. There were two shades of blue offered on USA import convertibles (all US imports were convertibles in 78) in '78. One was Barrier Blue (L52K) the other was Ancona Blue Metallic (L97B) which was available that year only on the Champagne Edition. Couldn't find Periwinkle Blue anywhere. Are you sure it's a VW color?
You'd have to discuss the paint matching business with the NAPA technician. I do know that the guy at my local NAPA took a couple of trips out into the parking lot to make sure his mix matched my color.
As for application.....yes, basically it's a sand and spray operation.
Mike
1970 Bus - The Ruptured Duck