Good question.
My Veloce is 390778 and has the same set up. It came with race style lap belts and hook eyes installed in the reinforced holesHi guys,
I have attached four photos showing the seatbelt attachment points on my Giulia Spider Veloce 101.18, VIN AR391066. This was one of the last USA Veloces. The top two photos are the left, driver's side, from the top. The bottom two photos are the right, passenger's side, from the bottom. Alfa provided these attachment points, but not the actual seat belts. The "hub" that is welded thru the floor is threaded for a M-10 fastener. I hope this is helpful to someone.
Don