Not sure if this answers your question but...
3 of the vacuum port caps are there as fitted by Triumph. The 4th (LH front on mine) is where the pipe from the AI pump would go. If the AI system is removed, that 4th port would have to be capped; apparently, the Triumph rubber is of a good quality and tends to outlast replacement rubber. Does this relate to your situation?
Note: I can't take credit for this, I've gleaned the information from these forums. :]
