I just came upon the same problem yesterday while fitting my booster on my 66 one ton. I actually went to the local u-pull-it to see if I could find a smaller unit off of an import or something. I don't care for those small chrome ones you so often see. I saw some fuel injection type set-ups on some of the cars that I thought might work......you know, the kind that have a formed hose that goes from the top of the throttle body, to a remote air-box. I haven't decided what I'm going to do yet.
Also did you find that when you mounted the booster, the rubber boot on the backside didn't protrude through the firewall enough to seal the opening that the pedal travels through? I need to figure out a way to seal that with a universal rubber boot of some sort, or the cold air is going to blow right on the family jewels........