Caelest

Pepakura Viewer is NOT gonna get you very far because you can not scale the pieces. Designer is the ONLY program you need in order to scale and print your armor.

I don't really know if the hayabusa add on will fit that well since that chest looks highly modified. You would have to most likely get creative and find a way to make it work.

The only other thing to do would be to get just the add on itself and using a 3D program, modify the hayabusa add on to fit that specific chestplate. If that's a no go for you, then ya just gotta get creative.