Yeah, took me about 3-hrs. Be sure to test harness often to make sure it still works. At some point, you actually have to bridge ground wires when removing interlock switches and diodes.
I think if I was to do it again, I would just build new harness from scratch with thinner-gauge wires and much, much smaller connectors. Here's diagram someone developed for using pre-gen engine in kart.
I actually completely removed ignition-switch and right-hand controls to replace with
one of these. I bypassed starter-relay and triggered starter-solenoid directly from switch. Was worried that higher-current needed may fry switch, but it's been 4-yrs and it's held up just fine.