I'd probably read a bit into what a wastegate actually is and does first. Any stock skyline turbo has a built in wastegate, external wastegates are only normally used on larger turbo's that require them.
http://en.wikipedia.org/wiki/Wastegate
Both an external wastegate and extrnal venting BOV are noisy and illegal. If you get caught with them you'll have to remove them and go for an EPA inspection. I would strongly recommend against it if your car is a daily and you don’t want cop attention.