The J Mod does not have very many steps in the sense that you need to take apart a million things, nor does it require any special tools that the regular DIY-er wouldn’t already have. All you need to do is drain the transmission, drop the lower transmission pan and remove the valve body. This in and of itself is not too difficult. Once the valve body is out, then you follow the steps and templates to remove the appropriate springs and drill the corresponding holes in the separator plate. Again, not too difficult. However, this is a job that requires precision. Using a drill is easy, but it is imperative that you do so accurately. Drilling too large or in the wrong spot could seriously hamper performance, if not stop operation altogether. Just make sure to proceed with caution, and read the instructions several times!
Speaking of instructions, a great repository (scratch that, the BEST repository) can be found on the Thunderbird and Cougar Club of America (TCCOA) website, under their transmission article section. It even features articles and comments by the great J-Man himself.
If you don’t feel confident doing this yourself, don’t worry. Any garage ought to be able to do it, or as mentioned, Ford dealers used to do it themselves back in the day. It should only take them an hour two, so it shouldn’t be too expensive.