Two Australian magazines(Electronics Australia & Silicon Chip) have
published projects for car computers in the last few years and both had
sources for two types of fuel flow sensors.
The sensor was positioned between the fuel return line & the injector
assembly (or carby)
Another thought, is the return line really nesessary or can it be blocked,
early model vehicals didn't have them. Maybe the flow pressure wasn't as
high ? My old jalopy has an electric fuel pump with no reticulation.
hth David