Ive laid under the my 65 staring at the space between the tank and rear end too, for a remote mount,,, I'm looking for options,, here is some dims off an offy manifold
manifold to tower 5 1/2"
engine block to tower 9 1/2"
bottom of manifold to cross member 12'

maybe the pic will help,,

http://s50.photobucket.com/albums/f320/fingersix/?action=view¤t=IMG_9778.jpg