Porting large applications to distributed computing platforms is a challenging task from a software engineering perspective. The Computational Grid has gained tremendous popularity as it aggregates unprecedented amounts of compute and storage resources by means of increasingly high performance network technology. The primary aim of this paper is to demonstrate how the development time to port very large applications to this environment can be significantly reduced. TOP-C and AMPIC are software packages that have each seen successful application in their respective domains of parallel computing and process creation/communication. We combine them to implement and deploy a master-worker model of parallel computing over the Computational Grid. To demonstrate the benefit of our approach, we ported the 1,000,000 line Geant4 sequential code in three man-weeks by using our TOP-C/AMPIC integration. This paper evaluates the benefits of our approach from a software engineering perspective, an...