Er-ruh…why do you want to do this? If you have a 325 in good condition, someone will happily buy it with funds that will go well towards a nice buildup of whatever 273-318-340-360 you might care to dream up.
With a good selection of Sawzall accessories and enough welding rods, you could certainly do this swap. Add extra money and time for the bigger brakes and suspension upgrades you'll need to make the car manageable with its screwy new front/rear weight distribution. Remember, the LA engine, of which the 273 was the first, was made smaller and lighter than the previous polyspherical-head engine with the immediate goal of fitting and working well in the A-bodies. There is nothing such as a "poly/hemi" engine.