Very early Ph1's have a return system to the tank which requires the use of a regulator on the rail. Later on they swapped to a non return system but used the same fuel rail blank, hence the regulator housing is still moulded on with the rail....however it is redundant.
Its pretty easy to tell which is which as the rail will either be blind or open into the regulator housing..........
172 Engine in the Rear of an R5 is that?