Check this out.
Found a picture with that ducting in it. Just to the left of the instrument cluster.
This is the drivers side a/c duct and I'll be damned if it doesn't match the catalog. This is factory air.
Center defroster ducts may be different (haven't got that deep yet).
Also checked the catalog I was in. It was the 57-66 catalog under the Accessories/Air Conditioning button at the top left.
So for a '74 it seems as though that ducting will work.

 

Above looks exactly like my 73 with Dealer installed AC. I thought it was funny because my finish panel is off right now after replacing a couple bulbs in the cluster last night.

Need pics of something specific? My heater core blew about a month ago and I was thinking about pulling it apart Saturday morning

 

Yeah, if you can, post a pic of the back of the register/louver whatever the heck you call it, with the hose attached. A couple of the guys were wondering what the clamp/clip looks like that holds on the ducting.
If you could measure the diameter, that would help also.
Thanks.
What I'm hoping is we can figure out if that ducting listed for other years in the DC catalog will work for our years.

 

No problem, I usually take pics as I go to so I can remember how to put things back together.

If I get to it, Ill see what I can do!

 

The U-Pick-It out here in AZ has a bunch of the '73-'79 dent sides with the duct work still intact. If you still need the ducts, I can go get you the duct and ship it to for the cost. If your interested let me know!