Hi
Mantain Production versions as per BOM combinations and Maintain the selection method in MRP4 view as 2 or 3as by production version, also define quota management for the same material in MRP2 as 4., then define the quota in MEQ1 for each production versions with the percentage for in house production.For a particular production version type you can give 100 quota, then in MRP run system will pick the that alternative.
Regards,
Anupam Sharma