I dont remember if it is the brush holder that is insulated or washers on the bolt is what insulates the brush from the case or both (been awhile since I did brushes). If you are going to purchase a new alt you might ask for one for an 85 M body (I believe) which is 78 amps rated. Might have the parts guy pull it & your choice & if they mount the same & the center divider is the std thick one & the price is right it'd make sense to go with that one