The "steelheads" invented the homemade integrated lines years ago and I am sure you can find better instruction in an older steelheading how-to book.
Basically the running line and the head are cut at a long diagonal so as to match up
They are then glued and sown together
Then the whole area (and a little extra at each end) is thread wrapped and coated with a layer of sealing glue
This sounds like a major pain in the ***.. and it is,
(that's why there are commercial integrated lines now )
but it's possible to build a line that does pretty much anything you want.