What motor mounts do I need for Magnum 360 in to 72 dart?

No those are for 68'-69'-70' B body and they are just the isolaters.The pictures I have included are a set of N.O.S. 340 block mounts which would be what you are looking for. Notice how the straight one is wider, that is the pass. side. The 318 driver side is as wide as the straight one, the 340/360 is narrower as shown in second pic.