That's a fair bit of power and the voltages are bordering on 'be careful you don't zing yourself'. You'll need to build such an amplifier carefully, good solid heatsinking, good quality output devices and no wimpy relays for speaker protection.
If it's a really old supply check to see if the transformer buzzes under load - I had some old transformers that I thought were good but they tend to bus which gets annoying.
One could build a nice amp with that kind of power.
Depending on your experience, you could probably adapt one of the many good DIY amps posted on this forum in the past few years.