All the upmarket machines back then were capable of providing a slapback, it could be varied according towhich speed was selected i.e. 3/34 ips for a slow repeat, 7/12ips for faster and 15ips for the rock & roll slapback. Some machines had vari-speed also that would allow more choice. Some machines a bit later ran at 30ips (inches per second) which meant eating the tape at a great rate ! All of these sounds were been used long before the earl Cliff & Shads stuff though, especially by the Americans, as you can hear with the Elvis, Buddy Holly & Eddie Cochran recordings to name but a few. Chet Atkins was one of the innovators at RCA and before him, Les Paul amongst a few. There was a guy called Ray Butts I think who built in a tape echo machine in the back of Scotty Moore's amp back in about 1956 (I think I read somewhere)
