You don't need a pressure relief in the front cover.
In fact, the worst thing you can do on a street blower IS have one.
Every time the blower goes into boost, if that case isn't pressurized, it is once the boost hits it.
When it gets pressurized, some fuel goes into the gear case. If you have a pressure release on the front, you release the pressure, and next time more fuel goes in when it hits boost again.
Rinse and repeat a few hundred cycles, and you've now contaminated your gear lube with fuel.
I tell anyone with a street blower to keep their hands off that pressure relief. They're hurting more than helping by continually removing pressure, unless they are frequently changing the gear lube out.
So, either leave it without a pressure relief, or put one in it and keep your hands off it.