Before you remove the spring seats, I would suggest that you get a angle finder and set it on top of the spring seat at 0*, then place the angle finder on the end of the pinion yoke to see what your pinion angle actually is and record it . That way you can install the new seats at the same angle.
also record measurements from the axle backing plates , and center seat to center seat.
Just don't put the measurements with the IFS instructions
There are some you tube videos on how to cut /weld new seats and set the pinion angle.