I have 1.25 spacers in the back with the stock rims, no problems so far. I installed them MY way and not what the directions said...
I know there was a member that bought the 1.25 spacer and had aftermarket rims and had to cut his studs. So you may want to go with 1.5 in the back..
I know they will also work on the front, But i do not need them.
Todd Z