When i had my gt28 conversion done many many moons ago
(by same tuner) mine didnt have a restrictor either,

I know all roller bearing turbos need them and i have one in my blouch turbo too,

I think i will get one for him then he will have to sort out warrenty for the turbo.....
And i will recomend fitting a better breathing system,

I think the cars putting out about 340hp (thats what it feels like to drive)
So an uprated breather system maybe needed....