Theres allways this way if your keen. Measure the length and count the output shaft splines. Then swap all the internals out of the donor case into your caddy case. Disadvantages- lot of work advantages- you get to check the condition of the parts as they go together. A turbo 400 is an easy trans to work on by its design it has clutch packsthat are enclosed, theres no frictions or steels located in the case itself. Just abit of wriggling and jigling and the whole piece just slides together. Just replace the pan gasket and the front and rear seals. I've done this a few times and I'm no auto tranny docter just using a will to get it done and some good common sense and reading a trans mission book and afew basic tools.