I replaced them on my pickup last year. I tossed the originals, but can measure the square plate on top. I also have a heater box in the garage, so can measure the hose ID. Stay tuned.

I have some spare ones if you need. I can measure tonight. One sitting on my parts shelf.

3 5/8   .   Duh. I'm sitting in my truck as I type this.

I checked and that will work great. If you have one for sale, I'm a buyer. And it can be your worst example, it will be reworked and totally hidden anyway.

Thanks!

That would be great. I'll wait to hear.

Prefectca wrote:

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This has peaked my curiosity. What are you trying to do Carl? Extra A/C vents?

Paul

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 No I've run into something that likely nobody will be able to answer, and that is whether or not a 1966 Canadian Pontiac could have been ordered with factory air and a manual transmission. My guess is "no" because there are no special duct pieces listed in the parts book or the assembly manual for a car with a clutch in it. I have exhausted my resources trying to find out if or how it would have been done. The US models are different, they came with a/c and a 4 speed but the entire pedal assembly as well as the steering column support are completely different design than the Canadian Pontiacs so I can't use their stuff.

When I got the car, Ken told me he had never had the a/c all hooked up (with the automatic) but it appears everything is there to do it. I did my 4 speed conversion. When I try to install the duct work for the left side dash vent, the clutch pedal and clutch fork pushrod are in the way. I am rerouting the ducting and I need to make a piece to angle the hose for the left vent up and over the steering column in a different spot. It looks like one of these pickup defroster outlets with some slight changes will be the perfect piece to do this. 

The one thing I did find was there is an early and late design on the Canadian Pontiacs for the left vent ducting and it involves deleting a plastic duct piece and using just hose, so I am doing that. I just didn't like their idea of squashing the hose flat in some areas to make it fit (as listed in the manual) so I'm using a slightly smaller hose and it will be easier to route it. I just need to have a way to adapt the existing duct pieces to smaller diameter hose.

Thanks for the explanation. I understand about the interference with the clutch pedal and I am sure that whatever you do to solve the problem will look like a factory installation.