The Boss block has special provisions to check oil pressure at the rear of the block. Ken fabricated this pickup that threads into the block and simplifies hooking up a pressure gauge. He prefers measuring pressure at the rear of the block because you can see the pressure as it comes out of the engine instead of before it enters. This way you know you have good pressure all the way through. Also, it helps clean up the engine compartment since there’s one less line that has to run from the firewall to the front of the engine.