Probably about a week after the first '63 Vette got totaled. One of the nice things about IRS swaps nowadays is that many of the donor cars can be had dirt cheap. Jag XJ6's up through 1987 (those are the ones that have the double coilover setup) can be found as parts cars for under a grand. Look around, and the IRS T-birds and Cougars can be had for half that, or less. The Jag front suspensions are an easy swap, too. All of those cars tend to have "rode hard and put away wet" syndrome, and by now, they're salvage yard material. Cheaper than a prepped 9" Ford nowadays.