Would something like this work? StarTech BRACKET Metal 3.5" to 5.25" Drive Adapter Bracket? is that all I'd need? -- http://www.newegg.com/Product/Product.aspx?Item=N82E16811993004
I'm assuming you need an adapter, does the maxupgrades kit come with one?
A word of warning to those who are going to use one or two of the ODD-SATA ports in MacPro1,1 (2006/2007). There is no space there between the fan box and the logic board for a conventional SATA cable. For a single cable you can use a 90° conector. If you are going to use two ports you should make a little cut out in the injection molded fan box above them. That is what I did. I used a metal saw to make the two parallel incisions and a strong carpet knife to make the perpendicular cut. I did not have a Dremel, but that would have been the best tool for that job. The material is probably ABS so expect its melting point around 200 °C if you plan to cut it with a heated tool. Do not over heat it too much.
If you use a standard connector and squeeze it between the fan box and the logic board there is the risk of bending the logic board and breaking an internal connection. Remember logic boards are 650$ a pop.
You also got to remember that the more you put into the computer, the more heat you will have in there...