I got a 1990 k2500. My boss has a an older i think 80s k20 that has a hitch he said he would give me. Does anyone know if the frame rails are the same space apart and if this will fit. Any input would be greatly appreciated.

 

i think your 1990 uses a wider hitch the older one should only be about 34 " wide

 

Things like that are very easy to adapt. Take it, and if it really is wrong, at least you'll have a few parts you can use when you do a correct installation.