1986 TRX350 Front End

Hello,
I have a 1986 TRX350 that has a pretty good popping sound when you are turning. I figured it was CV joints so I tore into it last night. It appears that the CV joints are well worn but still intact and functional. What I did notice is that the the differential had both front tires locked together. I got my son to hold one tire while I tried to turn the other. With a great bit of effort I could turn the tire but it did not sound good. Is this a limited slip differential in the front? What do you think the problem could be and a fix for the problem? Another note: While searching for CV joints for this ATV I noticed you can get joints for 87 and up, but I found none for the 86. Will the kits and joints for a 87 work on this model. I want to go ahead and put new joints in the front while I have it apart but I don't know what to do for parts.
I have several ATV's for me and the boys to hunt and play on but I really like this one and want to get it going.
Thanks for any help, and I really enjoy reading and learning from this site.
Thanks,
Rodney