Don't know if they are suppose to work or not, but my 84 had bad shafts too when I got it several months ago.

My front had worn splines also. All my spare parts are 86 to 94. I replaced both driveshafts with those newer parts. I know they weren't 84 parts, cause I have none of those, so I know some of the newer stuff will just bolt on.

Also I just did away with the rear carrier bearing on the rear, and bolded on a newer style driveshaft omitting the carrier bearing.

It's my daily driver with no problems!!