As I recall, those injectors fit quite tightly in the manifold holes. I also would question whether the top and bottom O rings got reversed. I wouldn't sweat the "used" intake gaskets. They're hard plastic and metal and don't deform until the engine gets nice and hot. I would question why the shop didn't follow the assembly procedures from Alpine, which has them installing the injectors and fuel rail on the manifold on the workbench, before it gets mounted on the engine.

Good luck! Your trials make my 14 hour installation look like a cake walk