Here is a picture of the correct windshield washer accessory on my '51 half ton.
http://s1116.photobucket.com/user/1950Cabover/media/IMG_0699_zpszwbxfrmk.jpg.html?sort=3&o=21

Note the silver pump body connected by hose to the fluid jar. The location of that part is important as it is located on the firewall in such a place that you can pump it with your left foot while driving. That is the only part that needs to be accurately located.
Here is a picture of my '50 COE with the Trico vacuum pump.

http://s1116.photobucket.com/user/1950Cabover/media/IMG_0700_zps8f39f3e5.jpg.html?sort=3&o=20

Note that the oil filter on the firewall is there only because it is a COE and would not be there on a standard cab. Thus, the washer bottle could go there. I think there is enough room for both on the driver's side of the firewall,
Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix