Gates info page:

https://www.gatespowerpro.com/Comergent/en/US/adirect/gates?cmd=catProductDetail&productID=42196037

Seems to good to be true, but Gates does make good products.

I think my car still has the original fuel lines due to the crimp type connections to the metal piping.

Also, does anyone know what the small metal cylinder is on the return diesel flow line? Line might be part # 1244767926 filter vent return hose

I don't know where the " too good to be true " comes into play, seems like typical good hose to me.

The cylinder "might" be a check valve to prevent fuel from being pulled from the return hose when the engine is being shut down. I've seen some industrial engines specify this. While it won't affect a pump where the shutdown is on the rack, it can affect pumps where the inlet fuel is shut off.

Primarily for this reason:

Approved for use with gasoline, diesel, bio-diesel including soybean methyl ester (SME), rapeseed methyl ester (RME), palm methyl ester (PME) per ASTM D6751, E-85, methanol, ethanol, ethanol extended gasoline, gasohol fuels and 100% alcohol

plus other 'Marilyn Monroe' attributes

Unlikely, since you didn't describe your vehicle. In this situation, a wag on a Dodge forum always assumes "1930 Fordson Tractor?".

I used Gates Barricade fuel hose on one of my 300D's (1984 or 85, forget) at the lift pump. I also forget if 1/4" or 5/16" ID. I bought at NAPA (per foot). It is stamped "rated for bio-diesel", so if it survives that, regular diesel is no problem. One guy here used PEX plastic pipe, which is impervious to almost anything. Sold for water pipe at Home Depot, but is quite stiff and needs special ring crimps. Might also look a bit funny on a diesel engine.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans