The largest common rear tire size for an untubbed 4th gen Novas is a 275/60 15. This size may require rolling the lip or moving the shock inboard depending on the backspacing of your wheels and the brand of the tire. Typically they slide right in with 4.25-5" of backspacing. Less than that will rub the fender lip. A 255/60 15 is a more conservative fit and plenty of tire if you're worried about it.
Fronts - I've run: 225/60 15, 235/60 15, 235/60 14, 205/70 15. Pretty much if the wheel goes over the disc brakes and you pick something around that height/aspect ratio you'll be fine. You might be able to get a little bigger tire but it will likely look stupid.
Remember that 4th gens have a wider front spacing than rear, so you're better off having more backspacing in the front than the rear, using a wheel spacer in the rear, or running a skinnier wheel/tire up front so they don't look like they're hanging out too far.
I can't speak to the larger diameter wheels. I can tell you that our cars work best with around 4 inches of backspacing with a 15 inch wheel. The 3" b/s wheels don't look or fit right.
This is 255/60 15 and 225/60 15.
235 60 14 all the way around with 3.25" b/s.
235 60 15 on the back, 215/70 front on my dad's 75.
295/60 14 on back, 195/70 14 front. They don't fit with 2.5" b/s wheels but I tried.
Same wheels fitting:
295/50 15 DR's. Don't really fit.
Hope that helps.