Could I put an aaz pump top onto a 1y pump without any modifications?
It's likely the exact same procedure as installing a LDA on a 1.6NA pump.
For that matter, why not just swap in the complete AAZ pump?
I may still deciding if I want to go na or turbo with it. Would a 9mm pump be ok woth na? giles pump?
9mm would be fine. It's what came on 1.6NAs so you don't have to worry about overfuelling.
You can't go wrong with a Giles pump. The one my brother has on his 1.9NA is great.