Did a quick Google search for the Rega 1, didn't find anything about tonearm wiring (IIRC, most turntables made since the CD-4 era [from ~1972] have low capacitance tonearm wiring), contacting Rega seems like the best option.
It may not be necessary to use the cables from JVC, CD-4 demods can compensate for 45kHz being lower amplitude than 20kHz, which would be caused by high(er) capacitance wiring.
Kirk Bayne