There's a 'right' way to do this and then there's the 'other' way. The right way is the most expensive, but will yield the best results. Buy a subframe from one of the manufacturers (I bought mine from Heidts), unbolt your factory subframe (8 bolts) and roll the assembly out of the way. Bolt up the new subframe in it's place. Your fenders, bumpers and everything else will also bolt right back on. You'll need to purchase a front suspension unit also, new or used, most people use the Mustang II. Steering will require a little modification, but not to difficult.
The 'other' way (and I've done this too) is to purchase V8 frame mounts for the engine if it's currently a 6 cylinder. These are about 90.00 from the aftermarket people. Then you'll need a special oilpan for the Nova because the tierod will interfer if you don't. The oil pan and pickup are about 125.00 from Summit. You'll need to cut out a section of the shock towers for headers, since stock exhausts would be even more of a nightmare. Reinforce the shock towers after you butcher them. The radiator will most likely be too small for a rat, I bought an AFCO aluminum radiator for 250.00. I also used a 4 speed which required some fabrication for clutch linkage. If you run an automatic, the job would be much simpler. The heater motor and windshied wipers will interfer with tall valve covers. You will have to use Hooker or Heddman fender well headers or make your own, like I did. The stock steering geometry will be your next headache. The steering sucked with a small block. A big block just magnifies the problem more due to it's weight. I have to admit, it took me a couple years to get everything ironed out, but boy was it fun when I did. I kept this car for 7 years and got pretty familiar with all the 'gotcha's'. If you decide to do this and need more info just let me know.