Yes, 68 - 74 Nova\Omega will work. I think there can be some variances from year to year with the location of the pump stops. Also, you may find that the holes for things like sway bar mounts and clutch z bar linkage have not been tapped. That was the case with the 69 Nova frame I used. So, I'd check them before putting the subframe in the car, even if you don't plan to use them, as its a bit more trouble to do it in the car. Also, as an FYI, the metal where the sway bar mounts attach is marginally thick enough to do the job and less so if you want to go with a big sway bar for more aggressive handling. I stripped on out while installing the sway bar. So, before you install the subframe, you might want to beef them up. A 1/4" plate welded in place would be a good solution. If it is on the outside, it would also serve as a spacer for the bracket as I think most aftermarket bushing brackets interfere with the lip on the spring pocket. I don't recall who, but someone here posted a thread with pictures on how he solved it without any welding.
Since mine was in the car already and only one hole was stripped, I just used a washer and lock nut on that bolt. Since it was closest to the spring pocket, I was able to get a wrench on it and tighten it down. I used a stubby wrench but I recall thinking that I probably use have used a regular sized one.