Stumbled upon this on another site and felt the need to share. It appears that 2006 Honda Civic coupe door weatherstrip works great on our 1964-1966 trucks. It pushes right on and fits without any modifications, per Rob Fisher here:
http://67-72chevytrucks.com/vboard/showthread.php?t=617703Hondapartscheap.com
They are called Front Door Opening Seals and described as Graphite Black.
Brand new in genuine Honda packaging was $38.92 per side.
P/N 72315-SVA-A01ZA, right side.
P/N 72355-SVA-A01ZA, left side.
Probably could get a good used set at the salvage yard for a 20 dollar bill.