I understand and I appreciate it. I think the system relies on a map signal and with a dual plan it could throw it off. But I haven't had any issues with air fuel ratio so far so I think the spacer is doing what it needs to do..
If your engine was still together I would suggest trying it without the spacer and with more spacers to see if it made any difference in the running of the engine.
PS. I am also interested because I am adding a fitech to my 340, and I am hoping to avoid such issues. I have an airgap, a Torker and Torker 2, plus the original iron dual plane that barely fits under the hood with the carb.