Both sets of extractors (VL or 31) will connect to the motor. The difference between them is purely how they fit the car. As you have an R31, you'd be silly to use VL ones, no?
And you will have no concerns about whether the R31 extractors will connect to your "catback" because you're probably not buying a catback off the shelf exhaust, and likely just getting a custom exhaust, no? In which case the exhaust guy will make it all line up, because.....that's what they do.