Digital / iPhone speedometer

I was thinking of replacing my analog speedo with an iPhone 6 Plus. I'm curious, is this practical and has anyone done this? My questions are:
1) what connector do I need and where would it plug into? I currently already have a power commander 3 so not sure where I can plug in one of those Bluetooth adaptors.
2) is there a good mount you've seen that would go in place of the existing speedo?
3) which app works best for this that also gives gas and GEAR

Thanks all!!