Dan is not infallible (or always available) and there are others here that are very good. I believe 1 member restores clusters as a profession. I don't know about darts, but 65 valiant use an external gauge regulator clipped into the back of the cluster. Here is one on ebay and I don't see an external reg or even a place to attach it. Maybe a different set of eyes can see it, or maybe it isn't actually a 65 cluster. Hope it helps
http://www.ebay.com/itm/1965-65-DOD...t=Vintage_Car_Truck_Parts_Accessories&vxp=mtr