One piece Floor pan

[314Chevelle]

Yeah this things given me hell. I figured Id cut & replace the front pan section since under the rear seat is solid. The front section will slide under the rockers but the rest of the pan has a lip facing down so I can't figure how to sit the pan flush. The lip sets downward & the rear seat section wont sit flat enough. Idk what to do 0. Is the front section suppose to slide under the rocker & bend the lip up in the rear & plug weld? Ugggh