That 80CFM tornado in the back is more than need for case exhaust. If its the CPU thats reacing 70C its definitly a HS problem.

If the HS is also about 70C then the fan is too small(which it is but not that bad). IF the HS is cooler then its not touching the CPU properly.

The HS only fits one way. The recess should be at the end where the CPU lever pivots.
You took the plastic film off the thermal pad right?