Hi Ed -
Don't know if you have bought the cats whiskers for your truck yet. I have heard that the cats whiskers from some suppliers is not curved at the back to fit correctly. I bought mine from The Truck Shop. It was bent correctly and came with the necessary staples.
I attached the cats whiskers to the interior window garnish of my '54 with staples. I used small 4" Vice Grip type pliers from Lowes to bend the staples over. Wasn't too difficult and I am pleased with the results.
HOWEVER ... the opening in the interior garnish on a vent-window truck like my '54 is wider than the garnish on a non-vent-window truck like your '49. Don't know if you can fit the little pliers in the space in your '49 garnish.
> [ CLICK] Here is a post about the process that I used.