Tony, The oil restrictor is the fitting that screws in the block at the back that the tube screws into, up till 1958.
In 1958 chev did away with the tube and made a new galley up the center of the block from the lifter galley. On that design the restrictor is part of the block, it is the size chev drilled the passage way behind the plug you will find in the center under the side cover.
I'm wondering why you would pinch the tube before the rockers? Did you feel you were getting to much oil?
