I've seen app notes suggesting a single PNP for the booster,
an NPN Darlington would impose additional headroom and
biasing circuitry I expect. Look at the National datasheets
and app notes for the LM117/317 and you'll find schematics.
At 30V drop and 5A, you'll be primarily interested in getting
the heat out - electrical performance is not the #1 difficulty.
You may want multiple, ballasted pass devices and forced
air cooling, or at least decent through-case convection and
a whole lot of fins.