In a 4L60E, then the Park/Neutral switch is adjustable. With the vehicle supported off the ground, providing adequate clearance to get to the bolts for the switch. With an assistant in the truck, the transmission in neutral, adjust the switch in small increments until the vehicle starts. Once it starts, tighten the bolts and attempt to start it again.
Now, if you have this entire switch off of the transmission, it may be difficult to get the switch back on properly and readjusted. Here is a link on how to readjust your safety neutral switch.