I bet it would be no problem. If any, older amps (made in the era when they did not have to cram-in 7x100W amps in a same-size cabinet) are more tolerant for low load impedance. Of course, if you still have the owner's manual around, it would not hurt to consult it. But I would go ahead and try! In the worst case, the amp will shut itself down and no damage will be made...