Jack..hopefully you take this the right way, but you might be part of the problem bud.
You cleared the codes when we asked you to pull them and tell us what you pulled.
Then purposely changed the #4 and #6 wires when the suggestion was #3 and #6 with the reason behind it being ok to swap 3 with 6 You purposely changed firing order to something that doesn't work.
I know with a little throttle these engines will usually start on 4 cylinder, seems kinda counter productive to do it on purpose though.
I'd really like to help you. Please follow the below
1. Fix the firing order if you haven't already.
2. Look at the #6 plug wire and ensure it is not laying on metal where it could arc out and that it'* not touching the O2 sensor or wiring. If it is a problem, correct it.
3. Try and start the car using a very little amount of throttle. If it doesn't start put the pedal to the floorboard to clean out the cylinder while cranking. As soon as it catches, let it back up. Do not over rev the motor.
4. See if your code reader still has codes stored. If so, please post them.
If you are serious about selling and we can't fix it up with you. Where are you located. I may be interested if it'* local.