Nope don't have to pull the final drive on these....That's the 350...Good news there. Just split the track and pull the sprocket.

This should help...
http://www.jdcrawlers.com/messagebo...order=asc&highlight=450b&start=0

Need manuals...
http://www.johndeeretechinfo.com/index.cfm?event=productDetails&product_id=40817&

http://www.johndeeretechinfo.com/index.cfm?event=productDetails&product_id=281576&#

With it not engaging like it should, I'd say you have a rust issue.
You've got a good machine...They're just a little touchy when it comes to steering clutches. They just need to be moved around from time to time, keeps things like this from happening. If you decide to get rid of it at some point, let me know. Love these old machines!
Good luck with it!