Ok well I went ahead an ordered one strip of steel 1/2"x7/8"x12" and another at 3/4"x7/8"x12. The driver's side spring is 2 leaves thicker than the OEM spring which brings it slightly more than 1/2" thicker than OEM and passenger is spring is 3 leaves thicker so about 7/8" thicker than OEM.

There isn't a lot of width there so hopefully the 3/16" of steel on each side of the 1/2" holes will be sufficient without being too thick to get in there.

If you look at the background of this old picture, you can see one of the gaps I am talking about on the passenger side.

Thanks for the advice so far on this! I will update next week when the steel comes in and I get the time to start fabbing this up.