nitrous ring gapping

The addtional ring gap only applies to the top ring. The second will be to stock specs so I wouldn't worry about blow by. The Keith Black pistons come with an instruction sheet that will tell you what the end gap factor should be for the intended usage.

FWIW, Hypereutetic alloy is much stronger than the typical cast alloy used in pistons prior to the mid 80's (90% of the engines made since the mid 80's have a hypereutetic cast alloy psiton) but it's not a strong as a forged piston. However, the hypereutetic alloy is much more thermally stable than either cast or forged so they can be set up for tighter clearances which results in less ring and cylinder wear. The hypereutetic is also harder so it wears less. The down side is that when exceed it's strength it will shatter where cast and forged will distort (a less destructive failure). If you keep the nitrious to reasonble levels you shouldn't have any issues. Look at all the Mustang 5.0's and LT1/LS1 Camaros and Firebirds running nitrious with factory hypereutetic pistons.