Its not a adapter, its a guide to re drill your rear hubs for a mustang bolt circle.
The front you swap to mustang hubs.
It opens your choice for wheels.
He used a adapter to make the guide because he is cheap and wont drop the coin on mustang rear hubs
I understand what he did, wish I could buy the drill guide to do this. I just do not have the tooling to make my own.
Then swap in front sn95's, drill the back and be done. I did find some adaptors on ebay so I may swap the fron and do the adaptors on the back.
I would suppose the new rims should then be 17's plus.