What kind of drive are you using? Obviously, a Bravo One drive application doesn't need a transmission, therfore a Stellings extension box for the Bravo One has a yoke type of set-up within the extension box which makes for no room for a tranny---but then a tranny isn't obvisously needed for a Bravo application as I initially mentioned. BUT, if you are going with a larger type of drive like #3's or 4's or 5's or 6's I think those may have provisions to accomodate a tranny.
Just for your info, IMCO makes an extension box without a yoke for the Bravo......they just use a longer drive/input shaft. Not quite sure what you are attempting to do exactly, but I suppose an IMCO extension box might be able to accomodate a tranny---but then the IMCO extension box is made for a Bravo. But the Stellings boxes have holes drilled out for 3 different drive heights whereas the IMCO does not.
I would think that you are refering to the extension boxes that are used for numbered drives as I have mentioned. I am not familiar with any of those, however someone might chime in who has some experience with them.
What are your plans?