I'd suggest that, if this is simply the power amp,
that you keep the heat sink, throw away the
components, and cobble up a modern "single
chip audio amp" in their place. But this may
depend on what's not shown, things elsewhere
in the radio that use the regulator, things we
don't know about what kind of amplifier (Class
AB or Class D?) and so on. But you should be
able to do better in today's components-space
for a decent solution. Go check the main players'
application-chooser-thingy that's somewhere
on all their product web pages, and follow the
yellow brick road.