For my 1994 Bonneville SE:
2 years ago I used Dorman #800-153 (3/8" diameter steel tube with compression fitting) and a tube-bender to near-exact replace the rusted-thru high-pressure fuel-line coming out of the filter ... this worked well.

Now, the parallel Return fuel-line (same location, under the P.*. rear door) is rusted-thru (sometimes I can smell fumes),
and, it looks like this Return-line steel tube diameter is a bit smaller than the 3/8" high-pressure line.

Can anyone confirm that the steel Return-line is 5/16" (under the P.*. rear door) ?

If the steel Return-line is 5/16" then I am thinking about using Dorman #800-154 (intending to cut-off 1 end of the beaded ends) to fit into the O.E. nylon quick-disconnect towards the rear (into the sender unit), along with Dorman #800-142 compression fittings for 5/16" tube diameter to splice into the OE steel Return-line that runs from the front.

Thanks for any info.