I see them occassionally on eBay, but I'd give some serious thought to running a Chevy 3 or 4 speed behind it. Theres a big difference between pony's and torque from a flathead to a chevy SB, particularly if its modified. That will also give you a good reason to step up the u-joints on the driveshaft as well. There's a reason we used to run Cad/LaSalle and Packard transmissions behind Olds and Cads in those Fords back in the day. You might end up needing to carry a spare tire and trans.