I worked with BillM on this amp via email: I'll paste his most pertinent response: It's a little disappointing, since much of the voicing comes from the TL072 op amps, not the tubes. You could say that the drive tone somes from the tubes, but the clean tone is solid state, but warmed up through the EL84s. They're definitely cathode-biased, by the way. I'm sure it could be modded, but I don't know what improvement you'd actually get. You could definitely find 47uF caps for C25 and C44, as long as they aren't too tall. It looks like they used a version of the Blues Junior power transformer, so I'm guessing that the TP24 will work, too. I don't know about the bolt spacing, though.