I've done the swap on my '89 and '92...The '92 had the same vacuum lines as the '94+, but the '89 didn't.
On my '89, the vacuum line for the diaphram for the bypass came from the driver's side fire wall. The small nipple in your picture (if the vacuum lines hadn't changed from '89-'91) is essentially an extra vacuum port. I ended up capping the one from the firewall as the supercharger came with the vacuum line on it for the bypass. But that one can be capped just as easily. So long as you have everything else hooked up properly.
Hope this helps a little.