Olympic plus to 70.3

This will get you there.  http://www.triathlete.com/2010/09/training/super-simple-ironman-70-3-triathlon-training-plan_12364

Swim & bike fitness and pacing have a lot to do with how well your run goes.  Granted, you need the run fitness to comfortably run a half, but if you're wiped out from the swim/bike, run fitness won't save you.  How did you feel coming out of the swim at your race?  Your bike time looked fine but you probably over-biked if you suffered on the run.  You'll need to dial the bike back.  If you monitor your effort with a power meter or heart rate monitor, you need to have a ceiling level for your effort that will still allow you to execute your run.  Yes, some brick runs after a 100k training ride will help. 

Two  things:

1.  Feeling spent after a race does not mean you cannot do a longer race.  I'm utterly spent after a 5K.  Also after an IM.

But,

2.  It does sound like you run volume is quite low.  Try ramping up mileage sensibly and you will stand a better chance of getting through that run.  If not, there's no shame in run/walking.  It happens.

Bonus #3:  Bricks are not really going to help, here, in my opinion.