Of course keep in mind though, it comes down to the armor and how well it fits in the first place, so it pays to still double-check your parts. Scaling a 110% on a standard 5'10 armor would hopefully get you pretty close for fitting at 6'4. If you do get lucky, importing all of those parts will give you a head-to-toe measurement to start overall scaling from if you can pull an overall height that way, you may get lucky and get 90%+ of your scaling usable just by doing that. Now if you are lucky on the particular pepakura armor you are looking at, you can import all of the pieces into the software and they will still be oriented in the correct positions (rather than all piled on top of each other). I'm 6'3', so I appreciate the scaling aspect when it comes to 5'10' scaled armors fitting 6'+ frames. In a perfect world, you can just go by what length looks good for you on your arm, and then hopefully that scale also has enough girth at the middle to fit your arm.

For instance, for a bicep, check the width at the widest point and overall length, and then scale according to your measurements. Your best bet is (as a beginner) to scale each piece, using Pepakura's point-to-point measurements to guide you.

Pepakura downloads