I really like the Alkali Widowmaker set too, the quality of the Alkali fins is unreal, really well crafted... but I think its probably a bit too much fin for the 7'2" or 7'7" Pintail, better suited to a rounder tail? (see pic below, beautiful fins)
The sides I have coming are more like the lower profile Bonzer sides, and so if I like them I think I'll likely go for one of these in a 6"...
"This fin was designed by the Campbell Brothers with the intention and specific purpose of being paired with their Bonzer Surfboards. This center fin is meant to complement the unique bottom contours and fin setups of their 3 and 5 fin designs.The Bonzer fin works synergistically with the additional runners to efficiently and effectively organize water flow across the bottom of the surfboard, resulting in a highly optimal transfer of energy. If you have a Bonzer board, this fin is the official prescription prescribed by the Brothers Campbell to fix it up for maximum performance."