I just got the response from our engineering team.
The document Intel MultiProcessor Specification v1.4 is the only one they have available, no updates were released after version 1.4.
This is an old document aiming for the multiple processor 20 years ago. Today, all processors are multiple processors and I understand there is no specific interrupt control available.
Processor technologies have changed a lot and I don't believe we are still using the PC/AT compatible mode or Symmetric mode, today, we use APIC.