73 dart, where to start

Oh wow. so after a butt load of googling, here's where I'm at. I've seen that a lot of people that add to the 225 are using a sanden 508, or r134 equivalent. do you know if that bracket is from a 189 or a 225? it looks like the bracket is going to be the odd piece. I found this:

Under Dash AC Unit Kit | Under Dash Air Conditioning Kits - Old Air Products - Underdash System

Which actually almost looks like the factory vent (well close enough) but it's not available with a bracket for my engine.