RPMs vs. Speed

So my speedometer is broke but not my tach.  I have a stock '60 Bugeye.  Can 
anyone help me relate a particular RPM to MPH?  Or if you can share the 
tranny and rear end ratios with me I suppose I could dust off the HP and due 
the math  myself.  I'm kind of lazy though.

Thanks!

Chris
'60 Bugeye

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