This paper presents an improved MIP approach for balancing paced tandem transfer lines with several spindle heads at each station. A spindle head executes a block of operations. The set of all available spindle heads as well as the operations executed by each spindle head, the spindle head times and costs are known. The problem at the line design stage consists in the choice of spindle heads from the given set and the assignment of the selected ones to workstations. There are operations for which several spindle heads are candidate (i.e. these operations can be executed in different combination with other operations). The goal is to minimize the line cost while satisfying the precedence, inclusion and exclusion constraints.