Vapor return or liquid return line?
My latest revision is smaller and inline with the return.
I dug up a bad picture of how I made mine. Similar to what was mentioned, but I made mine out of a barb fitting, a pipe plug, and a carb jet. I tapped the inside of the barb fitting for the pipe plug, then tapped the pipe plug for the jet. I tested a few different jet sizes to tweak the fuel pressure at the carb. My notes show that a .076" jet gave me 5.5psi and a .028" jet gave me 6.2psi at the carb. No restriction gave me 4.5psi.
My latest revision is smaller and inline with the return.