Making it intake from the top would help a lot since you have a bad airflow case and there is limited room for air to be taken in or exhausted on multiple sides. Making it take in fresh air even tho restricted will help.
However 75-77c isn't shutdown temperature. Measure it whilst playing overwatch then the gpu is also adding heat to the case. Or was that hw monitor during or shortly after playing overwatch? If that was during then you are NOT having temp issues.
I'd be a LOT more worried about that psu there. Wouldn't be surprised if that is causing an issue.