Seems like this lack of clearance problem with an automatic is not something new! I'm just assuming you're running a 235 with a stock front end. I tried running the manual drum/drum setup on my 54-3100 w/T5....with everything new it just didn't cut it. I went with manual front discs and rear drums and found them to be great!!!
You aren't going to find anything smaller than the 7" booster and getting a hydroboost setup fitted is going to present it's own set of problems.
The disc conversion is by no means without it's own set of problems....getting everything plumbed in properly, but you would not encounter the problems with transmission clearance and pedal linkage issues and you would have brakes that were a whole lot more friendly on the modern highway.
It may not be the answer to your problem but IMHO it is a viable alternative worth consideration. Hope this helps.
Dave
