What is the correct left defroster duct size for a non a/c 1974 Duster?

Hi Guys/Gals:
I'm going to replace the left defroster duct in my non-a/c 1974 Duster. I measured the defroster outlet on the heater box, and the left outlet (that goes up to the dash) is 2 1/4" outside diameter. The right outlet on the heater box appears to be smaller, but I don't need to replace that one. I'm not sure what the outside diameter of the vent in the dash (the one with the metal fastening clips on it) is. So what size flexible duct do I need? Is the dash vent also 2 1/4" outside diameter? I can't get a tape measure up there to measure it. A lot of places will sell you 2 1/2" flexible duct, but I'm not sure if this is the right size, or if there's an adapter that I need to put on the heater box defroster tube outlet to make this work. Ideas, anyone? Thanks.

The both dash defroster vents are 2 1/2. The one hose tapers down to 2 1/4. Hard to save the old brittle paper hoses if you don't know how to release the clip. Been saving them for a long time so when I build car I would have them.

I have seen repops for sale but not sure where.

The AC hoses are very pliable and have built on clamps you can unclip. I never tried an AC style on a non AC car . Always wanted to but never needed to.