If there is still enough insulation so you can identify colors, that's not so bad. Carefully mark the wires (perhaps by tracing them from where they were soldered) to identify them, and then disassemble the end bells from the laminations. You should be able to access the wires where they are soldered to the windings. Some new, properly colored wire, judiciously placed insulating tape, reassembly of the end bells, and you're set to go. I have not rebuilt a whole lot of them this way, but certainly four or five of them.
Another option is a new power transformer. The one sold by Dynakit Parts has a higher current capability than the original Dynaco transformer, which is operated very close to the limit of its capabilities, and runs hot. In the repair shop I had to replace two or three of the original transformers on Stereo 70s, including a dead one that was given to me...it now has the transformer from a Stromberg Carlson EL34 stereo amplifier that had been dropped; it's bigger enough that the Stereo 70's cover won't fit. I have kept that amplifier.