The springs and plugs control the pins that lock the slider in position after you adjust.
To run the car with no seat, either have a durametric to clear the airbag light, or plug in a seatbelt. You probably don't want to remove it from your removed seat (wiring hassles) but maybe you can buy/rent one from Woody to use. A dealer can also clear the code but I am unsure of cost.
When I did my WP I ran with the seat out and the cover removed so I could watch the belt, be prepared for a lot of heat and odd sounds, and for sure don't stick an arm back there if driving
