Is a copy of the contract that includes the buyer paying 60% of the price before production, and postponing the delivery of the goods and the rest of the price until after production, considered Islamically valid?

This transaction is called a forward sale (بيع السلم), and its conditions are: the full price must be paid at the contracting session, and the object of the contract must be specified in detail, though not present. The evidence for its permissibility is the hadith of Ibn Abbas that the Prophet, peace and blessings be upon him, said: "Whoever pays in advance (salaf) for something, let him pay in advance for a known measure and a known weight, for a known term." The described scenario—paying a portion of the price and deferring the rest—is not permissible. Nor is it permissible to agree that the purchased item be from the produce of a specific farm, due to the element of gharar (uncertainty/risk) involved.