I think that it is harder than we think this business of translating player's abilities to different eras. If we don't shift too much in time, OK, but I guess even in the eighties we cannot say much. The feel of racket/string/balls were too different. I guess Federer would have the edge, but...
The strings back then were able to generate much, much less spin. So one really had to control much more the stroke. Nowadays even an amateur player can hit as hard as he can with his eyes closed and generally the ball will land in. A heavy load of topspin and all balls tilt their trajectories downward. It is completely different with old racquets. That's the main reason old matches feel so slow, it is not that those folks had weak arms and wrists... so this would be the first new reality that everyone would have to adapt, and we can only guess how they would fare.
I think a guy like Nadal would have problems, given the huge amount of energy he transfers to the ball. I do not think that it is remotely possible to do that on old racquets. But this does not mean that he would not be able to find a completely different solution. Nadal's game is full of unorthodox solutions, from his forehand motion to his volley technique. But I still think he would struggle... on the other hand, some aspects of his game would translate nicely: the running forehand and, specially, his passing shots. Good passing shots are obviously important in a S&V environment. Also, he likes to have time to prepare his ground strokes, he would have it. The equation is not simple.
The main reason I think Federer would adapt better is not on his strokes, but his ability attack the net in a fluid fashion. He does not rush his strokes to follow them to the net, like a lot of players do, they simply flow. He naturally follows his drop shots to the net. In other words, he already does well on the basics aspects of 80's game.
As for Djokovic... I would like to see how his consistency would translate. One thing is for sure, he could trade back hand slices all day long...