A new square taper, or even a <shudder> Octalink chainset will look fine on that, the time it starts looking a bit odd is with HT2.
Having said that I have a 1982 (the only year they did them in 531) Holdsworth Avanti with a complete Ultegra 6600 groupset. Looks a little odd to the purists, but I am fine with it.
This is it with the previous groupset (Tiagra)
2009 Ridley Triton-T, full Ultegra
2011 On-One In-bred 29er Monster Cross
POS fixie, based on a Unknown steel frame.