Let me offer another perspective
At this point, you have spent several hundred hours and countless dollars restoring your GT500 KR
Is the type of originality gained by keeping 53 year old wiring in your car what you are looking for?
What would be the reason for keeping a 53 year old system in place after you have rebuilt everything else? Is $2,000 worth the piece of mind in knowing you wont have to tear the car apart a second time after the restoration is finished to chase some electrical gremlin? As a percentage of your total restoration costs, I suspect that will be pretty small.
Then as mentioned, there is the issue of brittle and damaged wiring
The reproduction wiring may have some slight differences, but it is new.
...and its been used by almost every 1968 SAAC Gold car over the last 15 years.
I will admit my perspective is biased, as I sold many of those wiring harnesses