On the 5.7L vortec engine, it is located underneath the upper intake manifold:
Note the location of the manifold bolts and studs before removal for reassembly in their original positions.
Do not disassemble the CSFI unit.
When installing the upper intake manifold be careful not to pinch the injector wires between the upper and lower intake manifolds.
fuel pressure regulator:
See Figure 1
Fig. Fig. 1: Exploded view of the fuel pressure regulator-CSFI systems