I proved this relieves a somewhat restrictive exhaust. My old S13 when it had a gt28rs i put on a 50mm wastegate with screamer and gained alot thought the revs and 20kw up top.
This was with a sr20 and a .63 rear housing.
And aslong as the wastegate plumbs in before the cat it should be "legal".
If u plumbed it in further past the cat it may give u the gains u want, by then the exhaust pulses have started to cool and there is more room available