seymouj
I would recommend you get the factory manuals. If your profile is correct you are looking for 1987 XJ manual. Go to the techauthority site and get the 800 number, call them and ask for your manuals. They only list the last 10 years on the web site but less than a year ago still had manuals for my 88 XJ.
Back in the AMC days, AMC had different manuals for engines, transmissions, transfer case, Chassis, and Electrical troubleshooting. I am convinced the electrical troubleshooting manual is worth it's weight in gold. Figure to spend $100 for the manuals since they are all seperate.
I then would recommmend a subscription to alldatadiy.com, it will have all the tech service bullitens for your XJ. They also have instructions and tech data for most jobs. They also list the cost of the OEM part and book hours to accomplish the job. The book time comes in handy to help you figure out how long something will take you. This will cost you $25 for the first year.
You can also pick up a chiltons or haynes for additional reference.
I have all of the suggestions listed, it always good to have more information!
Martin