Before drilling your floor pans, try using the stock rails. I always did, no messing with your floor(rust issues and metal colapse).
Keep your rails in place, sit the new seats over the stock rails and measure the discrepancy between the rails and seats. You could drill one side of the rails, and use metal plates to conect the OE holes on the other side (rail) to the seat holes.Or use 4 metal bars, conecting ea/ stock rail hole to ea seat hole. Or you could drill the seats to match the rails. Or you could bolt the seat to a metal bar(one for ea side), and these bars(one for ea side) drilled to match and sit over the rail.Several posibilities, according to what you have available(might be lucky and all holes match, or 2, check it out. Try keeping your OE rails, avoid as much as posible drilling your floor pan.
Later.________________________