Process/thread migration and checkpointing schemes support load balancing, load sharing and fault tolerance to improve application performance and system resource usage on workstation clusters. To enable these schemes to work in heterogeneous environments, we have developed an application-level migration and checkpointing package, MigThread, to abstract computation states at the language level for portability. To save and restore such states across different platforms, this paper proposes a novel "Receiver Makes Right" (RMR) data conversion method, called Coarse-Grain Tagged RMR (CGT-RMR), for efficient data marshalling and unmarshalling. Unlike common data representation standards, CGT-RMR does not require programmers to analyze data types, flatten aggregate types, and encode/ decode scalar types explicitly within programs. With help from MigThread?s type system, CGT-RMR assigns a tag to each data type and converts non-scalar types as a whole. This speeds up the data conversion process and eases the programming task dramatically, especially for the large data trunks common to migration and checkpointing. Armed with this "Plug-and-Play" style data conversion scheme, MigThread has been ported to work in heterogeneous environments. Some microbenchmarks and performance measurements within the SPLASH-2 suite are given to illustrate the efficiency of the data conversion process.