Looks like that would work well. And would be cheap to copy.The Volvo part acts as the main relay. You still need an ignition relay, possibly an AC relay, fuse and fuse holder, thermal switch (as mentioned), wiring, and connectors. These parts will add to the cost, but the two-speed controller is really trick.
This is an interesting writeup:
Wiring 2 speed fan with volvo relay. - SyTy/SGT - Forums
Wished I had known about this when I was installing a Mark VIII fan on my F-150.