I went on my 66 a factory style kit from a company called M&H. I bought it thru Year one. All the pieces were top quality. About $800 4 years ago. Not one bit of trouble.
I also bought the same brand from year one for my Demon. Same quality and a bit more in cost. But again. Top quality.
Aftermarket style harness I know little about. There are plenty of kits available but you still need to cut and put it together. Most people rave about them because you can upgrade the harness with better amperage’s for modern stuff like electric fuel pumps, AC, power windows, electric fans Etc. it all depends on your desire for your build.
My cars are period correct. Yours may be needing more dynamics to the harness than what my cars require.
For me, recreating a factory period car is more important than the fastest or most up to date car.