Help please asap!

This assumes that the 72 hasn't been converted to BBP. It will swap. Since the V-8 K-member will be needed, the easiest and fastest way to do the swap is to drop the entire assembled K-frame (engine, transmission, steering gear, suspension) through the bottom of the car. If rear on 72 is an open 7ΒΌ, keep what you have. If the 72 has disk brakes, the master cylinder and all underhood brake hardware will be needed.
X2 agreed - since I'm assuming here you'll have both cars I wouldn't get rid of the 72 for several reasons until the swap is complete. Also this would be a good time to clean clean and clean everything. Put any new gaskets and paint? since your thoughts are probably "more power?" This is the perfect time to ad any proformance parts you may have been thinking about ? While motor has easy access. Easy swap? Well yes, for someone who knows these cars well. For me - easy. For the "car guy" who bought the wife's 66 barracuda and paid $400 to have the freeze plugs replaced and looked at my duster and said "nice nova!" Maybe not so much....