That spacer is only really for when you want to run inline axles so that the wheelbase doesn't change.
If I remember correctly it will do strange things to your steering geometry.
What are you trying to achieve by shortening the wheelbase by that much? Maybe another adjustment would help more.
On the other hand just try running it like that and see how it goes
If you are new to setting up B4's this might be usefull:
http://www.petitrc.com/setup/associa...SetupHints.htm