Now on to the details.
Kevin's information on a generic throttle cable works if your just looking for a "plane-jane" functional control. A bit of web searching shows this reproduction correct looking
defrost cable with knob that will work and appear correct for your truck.
I couldn't find an original under dash mounting bracket, which would have come as part of the cable assembly when new, but I think this
generic under dash bracket should be useful in installing the cable. May need a few tweaks (original bracket had a slightly different angle - see pics below) but should work IMO.
See below for some info I found in my original 1950 Chevrolet Accessory Manual (1st picture - detailed location closeups) and an online 1951 Chevrolet Accessory Manual (2nd picture - better overall layout) for where the defrost cable control and heater "air control" (fan) switch was to be originally mounted. Since this kit was the same for 1947-53 (as well as the defrost control - original GM# 1990674) the diagrams and instructions apply to your 1949.
Hope this helps???
Dan
