~via BB (wap.pinstack.com)~
Your 8703 already is a brick!
The OS, though carrier branded, is rather inconsequential.
Your main concern is whether the build you are attempting to install has the code required for your device.
Unfortunately, I do not know about the 87xx devices or OS software (it's a brick!).
There may be an issue with the GSM / CDMA difference.
However, why are you wanting to change the OS? The 8703e is much newer than the 8700c.