Those part numbers are for the Tubing Splice on your truck to cut and splice into so you can run AN line and fittings on the filter.

 

Subscribing to this thread. I'm in the same boat, but for a different reason, my truck is Flex Fuel L59 which has a return line and a FF specific rail mounted regulator. I have the NNBS/TBSS manifold already. I want to keep the Flex Fuel capability so I don't know that going to the Corvette filter/regulator is the right way to go. I've been researching on and off for a while for pictures of how others have adapted the return style rail to a NNBS/TBSS intake.

I've also gone as far as picking up a rare intake from a 2005 LH6 5.3 which is the old style truck manifold, but it has the 4 bolt 87mm throttle body. I went after that because the return style rails from the FF L59 should mount on this one year manifold since it's a truck style manifold with a few changes. I'd probably still prefer to run the NNBS manifold as it seems there are other internal improvements over a truck manifold, but no definitive info I've found yet.

 

The only difference between the return and the returnless rail that is of concern is in the tune. The old Gen3 with the vacuum referenced regulator on the rail has a static Injector flow rate in the tune. The Gen3 mechanical regulator regulates the fuel with the vacuum signal. The Gen4 (returnless) is regulated through the tunes software and has a progressive fuel rate in the tune table.

This is an example of 50lb/hr flex fuel injectors with a (return) vacuum referenced regulator mounted on the rail. You can see the numbers are static throughout the entire table.



This is the injector flow rate table with the same flex injectors running the Corvette (non vacuum) regulator. You can see how the tune itself manages the flow rate vs the old gen3 vacuum referenced regulator.