It fit the 6300 perfectly and makes no noise.
I went to my local Big lot! and bought one of the 15" fan that you mentioned.
My F6.7K appreciate the air produced by the new fan. The radio does not turn the internal fan on. I am now noise free from the radio blower.
I operate mainly JT65 & 9 and the radio internal fan were turning on very often.
Thank you for the suggestion.
Ps. My original Extra license was N6LQ in 1976
It's solid and doesn't wobble at all - the weight of the equipment adds to the stability.
The rack looks like this: