DvP and the 1992 scam

Model a ready-forward deal between Bank L (lender of cash) and Bank B (borrower) for 15 days, settled (i) through a bank receipt and (ii) through simultaneous SGL transfer of securities and RBI current-account transfer of cash. For each design, list the states of the world in which L loses money and identify which party bears which risk. Then explain which of the following, introduced after 1992, would have prevented the fraud, and which would not: screen-based trading; a central counterparty with novation; dematerialised securities; T+1 settlement. Be precise about mechanism.