I got an email back from Bob Veasey at rustblue.com very fast. He suggested a higher humidity. I don't think I can get much higher than 85% in my sweat pot. He also suggested to pre-etch the metal in 10% muriatic acid. Without a blast cabinet, and reading the more detailed instructions on Mark Lee's site, this would make sense. The hardware store muriatic is 20%, so adding it to equal amount of water (remembering my high school chemistry). From what I read, a 30 second dip will remove all the current bluing, and lightly etch the surface.
I'm thinking of an experiment first. I blued an 03 floor plate after polishing to 320 at the same time as this receiver. It seemed a little light in color too. I'll doing a second floor plate polished to 240. If I don't like it, I'll try the express blue next, then try the pre-etching - pick the best method and do the receiver.