This really isn't a noob question, and for anyone who mounted a stock car seat who's pan isn't completely flat, I think they've all dealt with this problem.
The way I did it, is I measured the distance from each hole, then took a piece of cardboard and punched holes as a template. I put bolts through the cardboard and into the seat, being careful not to tear anything to make sure the template was correct. Once I got a good idea of where the holes were on the X and Y, I did modifications to the real frame. I used washers to pad any vertical differences between each mounting hole on the stock sliders. By the time I was done, it wasn't pretty, but the seat sat level, and I got to keep the functionality of the stock seat.
The top right of the photo is where my seat mounts. The big plate with the 4 holes was the original mounting points of my seats. The tube steel with the smaller holes is where the new seat mounted. Notice the front bar is angled. That was to save on time/welds and materials, as the distance between each hole was different.
In this photo, you can see I used washers to "level" the seat, as each mounting point was slightly different in height from the other.
Definitely the hardest part of building my rig. There was a lot of time involved, mostly "measure twice, cut once". Good luck!
