Personally, I think it would be easier without the harness. Unless you are going to hook up the alternator which does get a bit more complicated with a bit more risk IMHO. I just don't want the possibility of 60+ amps looking for a place to go. I already have plenty to do monitoring the engine itself. If you are concerned about the condition of the alternator, nowadays most auto supplies can test it for you free.

All you need are the ignition components and a few jumper wires to run it.

I just clamp the main starter cable to the positive battery post (Vice Grips will do) and then just touch the smaller starter wire to the same post to crank it. And as I said, I just use a jumper cable to ground it. Easy, peasy.