I disagree that cooling would be seriously hampered with the amp on its end with the bottom fins clear of the floor.
The cooling effect of the fins would only be slightly hindered by the different orientation. The fins would be at a slightly higher temperature than if in the normal position, but I bet not a lot more.
(I used to have two Carver amps I kept on end, they never had a problem)
The internal heat DOES rise up to the top end and that end is warmer than if the amp is laid flat.
It is not enough to just say 'bad idea'. Try it and see. Use a quality thermometer and measure the top fins temp compared to when flat.
I would guesstimate a ten to fifteen degree difference maximum in the center of the top fins. And the bottom (if raised off floor) would be about the same as in normal position.
Even a slight increase in the ambient heat of an electronic component can impact reliability over a prolonged period. Case-in-point, at work we had a unit called a Display Generation Unit which supplied video information to numerous monitors - seventies technology here. This unit was installed in an air-conditioned cabinet. The Mean Time Between Failure rate was horrible - just under 200 hours of operation.
We re-designed the cold air supply ducting to this unit and the Mean Time Between Failure rate improved to a little over 600 hours. The interesting point was that we only decreased the exhaust air temperature of this unit by under 15°F!
Operate your electronics as cool as possible - as for heat sinks, do not mess with their orientation as they are designed to dissipate heat efficiently.
Be well...