The length of the Dacron pendant is chosen so as to make the eye splices as easy to run home as possible. If the length is too short you will not easily run home the last eye.
In this case the chain is 3/8 inch and the Dacron is 5/8 inch, the nylon happens to be 3/4 inch.
After careful consideration of stainless swivels available "out there" I have chosen the Italian Kong which is INOX AISI 316 SWL rated at 2000 Kg because one can disassemble it and carefully inspect every aspect of the internals for any stress cracking or defects. I have dressed down any surface imperfections using a dremel tool and appropriate deburring attachments so that when assembled it easily swivels under load without any catching. I used Locktite to assemble it so that I can sleep safely at anchor
without concern about the single
strong fastener working lose under load or about any concerns of the threads corroding. None of the other swivels that I have seen on the market have these features.