The consensus seems to be that the quad cap should be replaced if it is an original. However, I think I will be a bit contrarian on this and say that as long as your quad cap is functioning properly, then it should not be necessary to replace it, though there is a question of reliability. But, I don’t recall ever reading much about damage to the amp when they do fail. Just make sure the fuse is 3A.
A few years ago, I ran an original Stereo 70 for a while with its original quad cap, until the quad cap failed (my fault for toggling the power switch too quickly). I replaced it with the 80/40/30/20 unit, which did sound better but not a total night and day improvement.
The 80/40/30/20 unit should not just be dropped-in and wired the same as the 30/20/20/20 unit. It should be wired in this sequence: 40/80/30/20. I think Bob might have a sticky or something somewhere with the wiring details?