how is it all plumbed- where is the pump in relation to radiator and engine? Where is the cap located? The cap needs to be on the suction side of the pump.

I don't think you can drill out the restrictors easily. I think they're located where the fittings are welded so would require some cutting/welding to modify them. I think it's in the top tube.

I'm not familiar with the Durango pump. How much does it flow? Is it wired through a relay so you're getting good power to the pump?