Level and secure the car
measure, measure measure measure WRITE it down.
You've then got a pile o spot welds to remove on the parts you're not replacing. Think things through before you cut! The time you spend thinking about the cuts you're abouit to make is very well spent.
Buy the new parts, might as well buy all theparts that surround them, too.
Using your measurements slowly, carefully reverse the procedure of removal.
That's a brief synopsis of the job you're about to take on.
Now, you've got to get to it!