AC/Heater Ducting - 68 Charger

[john108]

Hi
A long time has past since I took it apart.
I am getting ready to install the AC/Heater Ducting under the Dash.
I had to get replacement after market flexible ducts.
They don't have the latches that the original had and also the transition from round to rectangular are now separate pieces.
The original flexible ducts may have attached to the rigid ducts with, I think, flattened "Z" shaped clips. 
I am concerned that trying to use that type of clip would rip the flexible ducts when trying to install.

If those clips are recommended, do you know of a source?

Would you still use them or use hose clamps?
Also, when attaching rigid plastic parts together, what do you use?  Those "Z" clips could have been installed easily here.
I thought about drilling holes through both and installing a screw??
I hope this makes sense, if not, I can add pictures.
Thank You
John