Whoah.. that part 'don't say that you love me' isn't Stevie? He's really good at manipulating his voice to sound like hers. Especially since this was way back in 78 or 79.. I knew he did alot of that on the Tango album but not for Tusk.
I just assumed the first harmony part for the verses was Chris.. and some of the harmony on the chorus was Stevie. I do remember Stevie talking about him slowing things down and then speedin' em back up during the Tusk recordings in that interview for the recent BBC special about Fleetwood Mac Then she did that hilarious impression of him singing on the floor.