What I did with my old Holley TBI was use 2 conductor shielded cable spliced as close to the pick-up as I could and made sure the foil shield was long enough to cover the splice flush to the pick-up. I could not get a usable tach signal until I did this.
Most of the noise is inside the distributor from the spark jumping from the rotor to the towers.
MSD sells a 6'cable with their ends on it. If your distributor doesn't have
shielded pick-up wires you could just cut off the plug and splice it in like I said. The stuff can be hard to find unless you want 500 ft of it.
https://www.msdperformance.com/products/accessories/harnesses/parts/8862Kevin
