I got set up a few years back to build 727 transmissions. Bought a few tools, made a couple of fixtures and learned how to put them together. But then I got a little bit lost on some of the various permutations of seals and splines and decided that I wasn't quite ready to build parts for other guys since I didn't really know how to deal with a basket of random parts. I didn't have any problem taking a factory trans apart and putting it back together but if a guy brought me a box of parts pulled from different transmissions from different years then I was in over my head.