Anything's possible, but I wouldn't bother with major surgery.
I don't know about the 370, but I would be surprised if it didn't have the same setup as the concert...
Meaning, the concert has a power amp in jack in back. Use the preamp out to the new power amp, and put a "shorting plug" in the power amp in jack to ground the input of the internal power amp. A "shorting plug" is just a plug with the tip connected and soldered directly to the sleeve.