It's an interesting question. Changing to the Poly line would seem like a good move due to the fuel pressure. I don't know why Bosch didn't do it originally since they found it necessary for the other high pressure lines.
The spacer flange leaves a few questions. There are 2 parts, the one used first is closed, but with a later part number 911 110 264 01. The functional one used later but with an earlier number 911 110 264 00. It's strange to have a piece made for a hose, but not functional. Was Porsche working to eliminate the hand throttle sooner but held it up a while till they got it right, so made the piece for an additional air line but closed off?
I don't think using the flange without adding the AAV, AAR, etc would make a difference, and even then it seems you would want the spider pipe set up to be effective. With the 73.5 CIS you are a bit limited, as it is not available with the spider. The other replacement air boxes with spider seem to be one for '74-77 & '80-83, and the one for the large inlet '78-79. Spider only works with working adapter and AAR AAV.
