Are you able to make up a memcal to suit a 4.11 diff ratio VS V6?

If you have only upgraded the diff gears, then it wouldn't be necessary to edit the memcal as the car should drive fine without it (unless it's bouncing off the limiter before changing into the next gear, which we can fix). Your speedo would need to be recalibrated through, which can't be done via the memcal.