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There must be some error. The 0.1uF coupling capacitor on the audio input will attenuate most of the lower frequencies. Also the 10000uF caps on the opamp's input will short out most of the audio input to gnd. The ganged connection I think is supposed to be a dashed line on the drawing to indicate that feature.
The datasheet from national give the correct connections on pg6. Cc must be selected large enough to pass the LF side with minimal attenuation for good bass response (10-100uF) http://www.national.com/ds/LM/LM386.pdf
So many ready made & DIY guitar amps around....
Guitar hv few mV output so the amp should hv a matching i/p sensivity.
If you wish to DIY, here's one you can order & assembled yourself.
A straightforward amp.