specific standard spike hole 22 pattern such as the one illustrated in fig1 locking the offset of the mixing tips 96 in position allows the operator to move both injection devices 32 a 32 b in tandem with one another at all times hence once one mixing tip 96 of the injection device 32 a is positioned directly above a spike hole 22 the mixing tip 96 of the other injecting device 32 b will likewise be in proper position over a diagonally opposed spike hole 22 the degrees of freedom desired to move the injection devices 32 a 32 b could be accommodated using any of a variety of techniques one of which will now be detailed specifically the work head 34 of this embodiment includes a carriage 100 front and rear vertical support rods 102 extending downwardly from the carriage 100 and a swing arm support frame 104 that is movable vertically along the vertical support rods 102 first and second gauge and field laterally spaced swing arms 106 are each mounted on the swing arm support frame 104 so as to be swingable about a respective longitudinally extending horizontal axis 136 an injection device 32 a 32 b is mounted on the lower end of each swing arm 106 so as to be moveable relative to the swing arm 106 longitudinally of the machine 20 as best seen in fig6 and 7 the carriage 100 is mounted on an upper frame 137 of the chassis 36 by first and second laterally spaced longitudinally extending guide rail 110 each of which supports an associated sleeve 112 of the carriage 100 the carriage 100 can be driven to move longitudinally along the guide rail 110 by an electric motor 114 of the powered actuator assembly coupled to a rack.