Kevin, your link works fine. Nice truck BTW.
Try and remove as much,if not all the original black paint.
(It's tough stuff!)
I then used POR Metal Ready which neutralises the rust and provides a good key for the top coat and as Gmans 46 already mentions it likes 'seasoned' metal.
Here's a pic of my chassis after painting.
I brush painted and was more than happy with the results!

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.