I've used Hasselblad and Mamiya medium format cameras with FP-3000B just to learn about how things used to be done.

The main problems with this are that if you use something like Illford PAN-F Plus ISO 50 like I was, you have to do some stuff like take photos of a gray patch chart to see how much EV compensation (in addition to the compensation for the difference between ISO 3000 and 50) is needed for a correct exposure. For example, after the ISO conversion I found that I needed something like +0.5EV for the instant film and +1 or +1.5EV on my negative film (reading from from EV compensation set to 0 on my light meter.) This is because the real ISO of film is never exactly the even number it's supposed to be.

Also, instant film seems to have a rather curvy high-contrast tone response curve. Newer films will be more linear in their tone response. Therefore even if you figure out the exposure adjustments needed to get both films to expose the same for middle gray, the instant film will probably have poorer dynamic range and higher contrast compared to normally developed negative film, even if both are relatively modern. So shadows that look plugged and highlights that look totally blown on instant film may be perfectly acceptable on your "real" negative film.

In short, I doubt that instant film is ever going to show you exactly what you want and you'll have to spend some time figuring out what sorts of things that look bad on instant are actually OK on negative film.

Using digital for "proofs" is probably your best bet, but digital sensors tend to not have as good dynamic range as negative film that's exposed exactly +/-0 stops from perfect. So even then you probably won't get something exact, but it'll probably be much better than instant. Anyway, digital sensors tend to be very linear. Depending on how the RAW from the sensor is processed, you might be shown the "wrong" tone curve on a digital camera. I think most digital cameras tend to use a film-like gamma curve though so I'm guessing that will be close enough for most purposes. To do any better you'd have to match the film's tone curve in something like Adobe Camera Raw, and furthermore come up with some sort of single-shot "high dynamic range" tweaking to make the dynamic range look closer to film.

At least that's what I think the deal is based on my studies....