Magnaflow website shows specific part numbers for 4.6 2wd, 5.4 2wd, 4.6 4wd and 5.4 4wd.
Front and rears are also different part numbers and have all been changes to the 4xxxxx series for OBDII.
If a vehichle is in CA, the assembly must be replaced as a complete unit to be legal for mounting position, ID numbers and all. The law is a bit crazy but that's what Ca. does.
See the CA law on all this.
The code 420 is bank 1, 430 is bank 2.
Both are failing in about the same time interval.
Be wise to look at the activity of the rear sensor on both sides to verify the codes.
Also consider if anything was done to kill them such as the use of fuel additives etc.