I always thought the only improvement from the 1.6 to the aaz was head flow, and the dual stage injectors were more to reduce emissions and noise than improve performance. I know a few guys who swapped aaz heads onto their 1.6 but most avoided the dual stage injectors, although that might have been because they couldnt pop test them on a bottle jack.
I never looked into it that hard since I wasnt looking for that. It's been more than a couple years but I have been in giles shop a few times buying engines from one of his former employees. Nice place. Impressive equipment. Will send my pump to him when i get that far.