All that is required to link an SSI Contract to an Item411/Market Xpert Bid is that they both have the same name.
The easiest way to create a linked contract is to follow the steps in Creating Item411/Market Xpert Bids from SSI Contracts and to name the Item411/Market Xpert Bid ID the exact same name as the SSI Contract name.
Updating existing contracts, including scheduling updates, requires that the contract be linked to the Item411/Market Xpert Bid in this manner.