I'm pretty sure that big guy is Dave Prowse ~aka~ Darth Vader.
you are correct.
David Prowse
IMDB EntryLegendary strongman David Prowse (top) as seen in the famous "Ye Olde Wishing Well" sketch from Benny's first Thames show of Nov. 19, 1969. Two years after this appearance, he landed the role of Julian the bodyguard in Stanley Kubrick's A Clockwork Orange; but he is perhaps most famous for being the body of Darth Vader in the first three (released) Star Wars movies that came out between 1977 and 1983. He is also believed (bottom) to be the strongman who gets a lethal arrow towards the end of the Jan. 16, 1984 "Stupid Cupid" routine. Had also appeared in a 1968 episode of the U.S. sitcom The Beverly Hillbillies, and was Christopher Reeve's physical trainer for the first of the Superman movies in 1978.