Fuel rail spacers are special height depending on what rails and which injector was originally specified when ordering the manifold.
The GT fuel rail spacers are actually shorter. Plus, the GT500 injectors are shorter than the GT. There are a few possible combinations one could order.
Some aftermarker rails like the FORE GT500 rails need to be modified as they are bulky.
The FORE GT rails fit perfectly without any interference however rails would likely need to be dead-headed as little clearance to the alt would be available.