I'm looking at a 1959 Fender Bassman at the local shop and was wondering what some of the key things are to verify authenticity? Guitars are easy but I've never spent much time on vintage amps. I'm aware of the speaker code dating as well as the number on the cones in addition to the 2-letter code on the tube sticker, but how do you know if the electronics are original? Original caps? anything else? The amp looks pretty beat up but the shop says it's all original. What's the current market for a beat up but original '59, assuming everything is in working condition?