What have you been doing so far? I personally would do base and build in full and lose weeks from the specialty block but if you already have a decent base, then you might get away with cutting weeks from base.
The specialty phase has a taper built in (weeks 7 & 8) so you could do 1,2,7,8.
Also, join us in the Ironman in 2019 thread: The Ironman in 2019 thread