Floor pan replacement question

Hey Group,
I'm about to completely replace the floor pans on my 76 SB Vert and would
like some pointers from some of you who have done this. I know you must take
a multitude of measurements before cutting out the old pans so that you get
the bolt holes in the right spot to fit the body. Are any of the frame
locations better to measure from than others? Are there any hints you can
give me so I don't have to do this more than once? Any web sites with pics
of the process?
Thanks in advance,
Charles