Creation Of Production Order without PP module

Hi PP guru's

There is one Specific requirment from Client side, the Requirement is

They are not supposed to implement the PP module in R/3 but they want to get generate the Production Order in R/3 through some interface with lagacy system, based on that they want GR at warehouse,They are using MTS system

They are doing all Production Planning in the exiting Lagacy system and the production Order will be created via interface from those system

for that requirment what master data are requred so that we can full fill the client requirment

valuable suggestion will get awarded

Thanks in advance