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It should be a fairly straight forward swap, if you have the accessory brackets off the 72 engine it would be easier. Motor mounts will not be an issue as long as the 67 was originally a 326 V8 car. If it was a 230 OHC6 car things get more complicated. If it was a 6 cylinder car, and you have not done engine swaps before I would suggest getting some help. Besides Motor mounts, the fuel line will be on the wrong side of the frame, as will the Battery tray as the starter is located on the passenger side on a OHC6 & the drivers side on a Pontiac V8 (fuel pumps are also on the opposite sides)
Things you may have to do are add a bigger radiator, I would consider a transmission change as well, I am assuming the car is an automatic, the stock 2 speed ST-300 will bolt up and work, but you will not be happy with the performance as there are no performance Torque converters available for them. I would swap in a decent TH-350 3-speed trans. almost a bolt in.
Post some pic's of the car & engines, and some more info.