For those who have 85+ model year vans, how long is the wiring harness from
the firewall passthrough to the furthest point on the engine?

I'm relocating the ECU on my 84 to under the rear seat and will be drilling
out  a hole for the passthrough, but trying to figure out if I can use the
wires I have (if the length is under four feet), or do I need to buy a
large roll (if the length is over four feet).