89 camaro heater core

i really dont want to pay $600+ to replace my heater core. when i could pay $40, buy the part & do it myself any suggestions on good manuals for DIY?
i heard Haynes or Chiltons are pretty good any estimates on how much time i'm looking at spending on a project like this?
i also have no air coming out of my air ducts i think its a simple error from my previous mechanic any suggestions or re-hooking it up or diagnosis?
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