The blue alternator fan/pulley, as far as I know, was used on June and July 1965 Dearborn cars. I believe Jeff has also documented some San Jose applications, but I'm not sure what the window of production is when they were used. I don't believe your April build is applicable if you want to be correct.
As a sidenote, if you're wanting to use the blue fan/pulley to be unique, be prepared for a lot of questions and raised eyebrows with regards to the authenticity and originality of the color. Documentation like this helps
but there is still, probably justifiably so, skepticism. My original fan/pulley were blue, and I had a good amount of original paint on the back of the fan to match to, so I don't have a problem with it.