The paper deals with the minimization of the number of pieces of equipment for transfer lines with multi-spindle workstations. The preliminary design stage is considered. The machining operations are grouped into blocks. Each block executed by one spindle head. The relations of the necessity and the possibility of combining operations in blocks and workstations as well as precedence constraints are given. The problem is to find the best assignment of operations to blocks and to workstations, whereas minimizing the number of pieces of equipment used. The solution must provide a desired productivity (cycle time), it must also satisfy precedence and compatibility constraints. The problem is a generalization of the simple assembly line balancing problem. A combined heuristic approach is proposed. It is based on decomposition of the initial problem into several sub-problems and solving them by an exact algorithm. Results of computational experiments are presented.