Hi Don,firstly welcome.
You mention both the door seal and the cab windlace.
They are two different things.

The seal fitted to the door is technically 'one piece'and is glued on,and also has a lower metal retaining strip screwed to the bottom of the door.

There is a cab windlace that goes around the door opening,and a lower windlace that's retained by a metal trim screwed to the floor section at the rocker.
Therefor, I would assume this is two peice.

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.