In addition to the above wise suggestions...
Customary wisdom says not to use a device at more than half its rated capacity.
Therefore the project uses five 2N3055 so each delivers 8 amps. This gives a cushion for the unexpected, such as marginal heatsinking, excessively high voltage from the transformer, heavy load, leaky filter caps, accidental short circuits while the enclosure is open, etc.
Notice that each also has a low ohm resistor in the emitter leg. This is to balance current flow through the five transistors. Thus eliminating the risk that any one transistor might be so out of spec with the others that it could hog current and burn up.