What's the budget?
A 60V CT, 5A transformer alone isn't going to be cheap. A specialized power supply containing such a transformer, much more expensive still.
It could be dangerous for someone new at PSU design and implementation but on the other hand it's not necessarily more dangerous than ??? (anything else). As with any custom PSU, already there's the element of the high voltage and amperage input. One must take similar care in dealing with the ~ 60V transformer output too.
If you could settle for a lower amp output, the price of construction might go way down. For example a 120VA transformer for only
$11 here, (60V CT [center tapped] would be your target?) and since it doesn't need be regulated (at least according to the article it doesn't), it would simply be a matter of rectifying it and putting a couple filter caps after that... I didn't look at the rest of the amp, perhaps it has the caps already, do recall some mention of 10,000 MFD.
With a little forethought, you could even put together a Tread or Steps to regulate that, just make it the minimal voltage drop possible to reduce costs of the regulator, and of course appropriately rated caps and diodes in the design. It'd just need more scrutiny to make sure nothing is amiss before powering up. You might email the author of the article for examples of what s/he feels will work as "unregulated" is a pretty large variation in voltage from an unloaded PSU.
As for the 5V, consider it a second power supply inside same chassis.
Since it's relatively easy to find higher voltage caps and diodes, mainly the hunt is for a cost-effective transformer. You will probably need to build this rather than buying one, I dont' recall seeing too many +/- 30V 5A supplies ready-made... none actually but then I wasn't looking for them either.
