I now believe that what I thought was an ALDA on top of your IP is probably the IP's round vacuum actuated IP/engine shut-down device... and the vacuum line that leads to this device comes through the firewall from the ignition switch.

I have also made out what looks like a restricted orifice between the " Y " connector and what I believe is your VCV on the left side of the IP [ an unusual location for VCVs].

Regards,