Cruiser machinery in Unicorn and light carriers

Did HMS Unicorn and the 1942-program light carriers use cruiser turbines and boilers?

Broadly yes: large cruisers and small carriers used closely related machinery, though carrier installations could include weight-dependent changes for their operating conditions.

Larger cruisers and smaller carriers used substantially the same turbines and boilers. Carrier installations could include additions that a cruiser's weight limits would prevent. Those differences could allow slightly different operating temperatures, even where the basic machinery was closely related.