I am a little confused.
A TT Wiring would be a Power Chord ?
A Tonearm Wiring will be mostly a Internal Tonearm Wiring Loom within a Tonearm Wand, which will have a added Tag Wire Interface at the Headshell end to connect the Cartridge End and a Phono Interconnect Interface at the Pillar End to connect the Wiring to the Amplification in use.
As the inquiry is referring to the RCA Connectors I assume the Cable at the Pillar to Amplifier is to be the cable that is an upgrade.
Is this a 5 Pin DIN to RCA Cable ? or is the RCA Female attached to the TT's Plinth and a RCA > RCA Cable is able to be used.
In either case there are endless options at a broad range of prices and the used market is well worth an investigation as well.
Limiting the choice to an offering from one individual will not enable to see how different Cables used at the Interface can impact on the performance, and be considered an upgrade to the ones being replaced.
Does the Cable Builder referred to have a assembly that can be offered for a trial/loan period ?