Say X makes an agreement to sell a certain awnings to Y. The agreement provides that Y will pay in 2 installments and that no property shall pass to Y until both payments are made. (This is somewhat like a hire-puchase agreement.)
The agreement also provides that on default by Y, X can enter the premises to remove the awnings.

The nature of the good is that it will become a fixture to the building.

What kind of right would X have? How would you class X’s interest? Equitable? Would it be proprietary (on account of the fact that the awnings have become fixtures)?

I am assuming that this is Torrens land and the dealing is unregistered.
To clarify:
Y has possession. But that does not mean property (as in title) has passed to him. Y does not get title till payment of both installments.