I have the opportunity to buy a Blackface Bassman with an AA864 circuit. I have been told that these are the best sounding and rarest of the Bassman circuits. -I previously owned an AB165, what will the difference in sound be? -Should I be worried about the reliability of a 40 year old amp? -Any comments on about the originality/authenticity of the circuit? -Any comments on the AA864 in general, any recommended mods (it already has a 3 prong chord)? -How well will it take to fuzzes, anywhere as well as a Marshall? -Finally, about how much should I be looking to pay, what would be a good price?