This
1939-46 door weatherstrip diagram page from Steele Rubber has a breakdown of the different door/cab door opening weatherstrip components. The piece you are showing is the door weather strip seal (Steele# 70-0145-73) that gets glued on to the door itself. What we all call the door "windlace", Steele calls a weatherstrip (Steele# 60-0054-73) that gets attached to the cab door opening and the round tube edge contacts the door when the door gets closed. It's held to the cab door opening with metal strips that sandwich the "windlace" to the cab as seen in the small screen grab below from the Steele page.
As far as installing the weatherstrip you have to the door, most folks start and end at the bottom center of the door, using a continuous strip. The two ends at the door bottom get cut to butt up against each other and you can use the adhesive for mounting to the door to join the butt ends. Just be careful not to apply too much adhesive to join the ends. Any excess that may get on the face of the weatherstrip can get stuck against the cab door opening when closing the door (if not fully cured), resulting in possibly tearing the new weatherstrip off when you go to open the door back up.
