Take a look at this:
http://www.conestogadiesel.com/support/fuellineroutingoptionsforfordidiengines.html
This is from Conestoga Diesel (Mel). Use the top diagram, and that will work. Ignore the one going under the turbo........
The main point is, as long as all 8 injectors, the IP and filter are all connected to the return line to the tank on the drivers side rear of the engine. The return line in the split loom conduit is some PO home brew. You are getting too hung up on that line under the turbo. The main part you need to be concerned with is getting the lines to the TEE on the drivers rear...... Forget/abandon that line and run all new. The configuration of the lines is not important, as long as all 8, IP and Filter have a path to the tank......
Heck, you could start at #7 under the turbo with a dead end cap, connect them 7,5,3,1, across the front and tee in the IP and Filter, up by the IP, the down 2,4,6,8 off to tank....... That would be the most complicated, but it would work.... For a turbo application, I would use the top diagram on the above page, you would be good to go, and have to interact the least under the turbo/air box.....
For ease of use, and for future searches, here is the diagram I am talking about: (Thanks Mel)
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