The diameter of the line doesn't matter-- - - - -1/8" to 3/4" will transfer the same pressure. The only difference will be the volume of oil it takes to fill the line. Where are you connecting the pressure line? It should be plumbed directly into the port on the driver's side rear of the engine, down near the oil pan rail. On most engines, the oil filter supply line is teed into the same port with a fitting called a "street tee".
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!