So...

...this 500VA 35V-35V transformer would let me connect the two outputs in series to get [email protected]. By the time it has lost a few volts through the additional components (rectifier etc) I would have 68.6V (I think it's 1.6V drop for suitable rectifiers?). This 30V-30V would give me 58.4V - with 57.2V being the minimum rather than the optimal that I had thought it represented - so it would be the bottom line option.

Daft question, is it feasible to knock the output down a bit from a transformer, short of fiddling with the number of turns?