I was gone for a bit. To try to answer some of the questions:
On the 67 IPC documentation that I know of, nothing indicates that the IPC's were ordered as COPO's. The 'fleet code' does appear on the paperwork, which shows the cars were ordered thru the Central Office / Fleet & Special Order office as some type of special order. But no COPO number or other COPO indicator appears in the documentation.
There were actually 12 L35 Canadian IPC's. And at least three (including Jeff's) of those cars do not have a fleet code on the tag.
80055 is basically the dealer code for the Oshawa zone office. It does appear on other non-IPC cars. I'm not sure what GM of Canada says 80055 means now, but I recall seeing the definition vary.
All cars were built on the assembly line. There was no alternative off-line assembly process nor the room to do such.
I'm not a 67 Yenko expert, but none came from the factory as a 427. 69 was the first year for that.
I agree with Jeff, the 5 group dash probably just means 'special order - see instructions'.
Normally seems to refer to paint. Has to be Fisher Body related since Chevy never looked at the tag.
Hope this helps...