Aperently the boster on my 89 XJ is bad (vacume leak) I want to upgrade to the later model (double) but not sure what year to ask for and what changes I need to make.

Can somone direct me to a web site with this info or tell me what I need to do?

Go to the tech section at www.madxj.com If you use a '95-'96 XJ booster since it doesn't require the rod to be changed.