Thanks for all of the responses. I actually started working life as an electronics engineer and have, through "hands on experience" of various voltages/currents, learned a healthy respect for electrickery. So don't worry fellow PPRuners, not about to fry myself!
I was thinking about using a variac but from the posts on here, it seems light the blue touchpaper and retire is the way to go ;-)
To answer specific questions, I have no idea of the specifics of the caps, having never opened the boxes but the total RMS of the power amp is around 800w so they might be as big as .05F, maybe 0.1F so a healthy belt if they do let go. Probably standard dielectrics, doubt there's any oil in there.
The boxes have been in professional storage, low humidity and fairly constant temperature so I'm not concerned about condensation or corrosion.
I'll let you know if the results are "interesting"
