I looked up both the 69 fullsize chevy and 69 Canadian Poncho brochures and noticed that Pontiac track is (frt-rr) 63.5", 63.4" but a fullsize chevy is 62.5" and 62.4". Since both cars are otherwise identical mechanically you would think it's the wheel offset. The original wheels on my 2+2 have about an extra inch of negative offset (inch less of backspace) compared to standard GM wheels of the era. Since track is measured from the center to center of the wheels then adding an inch of negative offset would move the center of the wheel by 1/2", increasing track by one inch total.

So either canadian pontiacs had different offset wheels or they made a baldfaced lie about having more track than a chevy and marketed that lie heavily.

Yes, 3401978 is the ornament, the actual small piece bolted to the 3901712 hubcap. The parts book shows it fitting 68 as well but for 67 it shows 3401977, "Disc Brakes". The 3901712 actual snap on cap is the same 67 to 79 and also fits 67 Chevrolets with rally wheels.

Here's a photo of the "Disc Brake" center caps.  I understand they're correct for 1967 only, and there seems to be a debate as to whether it's correct to be on the front wheels only, or on all 4.

I came across these a number of years ago, first 2, then stumbled across the other 2.   I sold them on ebay a couple years ago, didn't get near what I thought I would.

Yes, I have a complete set of 1967 rallys from a disc brake car and they have just "disc brakes" on all four.  They were 15" by 5" which for a big old barge like a 1967 2+2 seems pretty inadequate. 

No. I'm kind of saving these to sell with a 67 Grande project package.  The ones I have on my 66 are 15x7's with the 66 Grande wheel cover spinner adapted to the centre cap.

Sorry to hear of your father in law.  I've been dealing with similar lately.