@Will-i-am
Bad idea. You'll end up with crippled system.
If you really want to install 1.3, you need to wipe traces of the OS 3.x first. Even then, some parts of the 1.x will misbehave with too fresh KS ROM.
WB 3.0 will work just fine on KS 3.1 though, but you'll miss couple of fixes SetPatch 40.x added, and obviously the features added in WB 3.1 over 3.0.