The drop link ball joint on my 92 Defender has failed as the rubber gaiter has split. I decided to get a new drop link as well as the ball joint replacement kit just in case I end up having to cut the old drop link off. BUT..... mine has a 6 bolt steering box instead of the 4 bolt and the drop links are different even though the ball joint replacement kits are the same. I've been advised by our main dealer that the drop arms for the 6 bolt boxes are now obsolete. I've googled and used searched but can't find a definitive answer - are the 4 bolt boxes directly interchangeable with the 6 bolt ones? If this is going to be an issue in the future I might as well splash the cash and get a 4 bolt box now. Cheers all.

Yes they are. I swapped my 6-bolt for a 4-bolt.

Yes,I have done the same.

Thanks guys. Assume it bolts to the chassis directly without having to drill new holes?

Yes, straight swap. Get new lock tabs for the bolt heads if yours has those.