First I am using the 700R4 from a 92, so its not the electric 4l60, and its not the older -86 (problematic). I only run a single 4.7 case, at one time I was gonna go duals, but since the 4.3 was installed I havn't really needed them. As far as motor mounts, make your own and make them beefy or use these
http://advanceadapters.com/category/...e+Mounts+.html
I think if you run stock duals you will be stoked, and it will save you a little money.