Abstract: An engagement assembly (1) for mounting to a first head block (2) so as to engage a Second head block (5), the assembly comprising: at least one mounting bracket for mounting the assembly to the first head block (2); a plurality of extendable members each connected at a first end to the at least one mounting bracket, a second opposed end of each extendable member being extendable away from the first head block; a plurality of engagement portions (50 A,B) in communication with the second ends such that extensions of the second ends consequently extends the engagement portions (25), the engagement portions adapted to engage engagement brackets (30) mounted to the second head block (5), wherein on engagement the engagement assembly permits selective relative movement in the horizontal plane and free relative vertical movement.