I bought a Shad 50L from Murph and it comes with a standard mounting plate that is made of stamped metal and a plastic cover that fits over it that has rubber bumpers that the top case rests on. If you have a proper rack IE: not the stock plastic crappy junk that come with the bike but something like what Phil makes. Check out philsfarkels to see what I mean. There are others out there that will also work but I made my own from the same type of material and design type that Phil did (thanks for the inspiration Phil). The most important requirement is that it is rigid and large enough to hold a large case like the 50L Shad. If the rack has been replaced you do not need to order anything else, what Murph sells you will do the job but like Phil said he sells the tee nuts that really make the job simple. If you do not have access to a cad design program and vertical machining center like I did, the rack from Phil is a steal for the price and really looks great when you remove all the mounting base stuff that holds the top case! 
In my opinion the Shad is the best case for the money, it come with the mounting plate and the back rest cushion that most others charge you for.
Okay, now we are getting to what I am actually wanting to know. So if I use Phil's rack, as asked in my original post, it sounds like I won't need the mounting kit from Murph. Is that correct?
Thanks,
Phil
