OD tranny hard to come by?

thanks for the hint. yeah ill eventually be installing into my 70 dart but by the time i will install, i hope to finish school and have the tools and experience to make the modifications....or perhaps just find a someone here near by to help me out!

is the OD worht the modifications neccesary to install? im mainly doin it so i can run at a lower rpm, thereby increasing fuel economy.