ROLA 66 tape recorder

I have just acquired Rola 66 tape recorder and am considering restoration. One thing I want to do would be to change tape speed. My unit was made to run 7.5 inch/sec and I would like to change it to 15 inch/sec. To do that I need to change the thickness of the capstain shaft. Does anyone have Rola 66 that runs on 15 inch/sec and could measure capstain shaft and post that measurement.
 
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Never knew they made a R-R.

dave