Product changeover is becoming increasingly critical in planning assembly capacity which may be manual or automated with supporting part-holding and conveying devices. The basic choice is between assembly systems that are more product-specific, such as dedicated assembly heads, and those that are relatively flexible, such as manual or robotic systems. A rigid system would require frequent transitions as product variety increases, and may nullify any scale economies. A flexible system, on the other hand, though more expensive, can incorporate product changeovers more easily and would therefore require less transitions, creating scope economies. A quantitative analysts to study such interactions of system parameters with a view to developing understanding and procedures for dynamic planning of flexible assembly capacity is the objective of this paper.