The starters for the six and the v8 are exactly the same EXCEPT that the starter drive gear for the six has 9 teeth and the gear for the v8 has 10 teeth. If both of your starters have 10 teeth you were using the wrong starter gear in your six. The problem with this is that he ten tooth gear will not engage correctly with the six cylinder ring gear. This forces the ring gear forward and partly off the flywheel and is probably the cause of the interference problem with your mini starter. The relationship between the mounting plate and ring gear are exactly the same distance on the six and v8. The mini starter can probably be made to work in your six if something is done to move the starter away from the ring gear a small amount say 1 sixteenth maybe. Before doing any grinding, check the position for the ring gear on the flywheel and make sure it hasn't been moved forward by the wrong starter gear. Probably not a good idea to hammer on it to get it back to where it belongs against the flange where it will not interfere with your mini starter. This problem of the wrong gear is common, best way is get the right 9 tooth gear and use the original type Ford starter. Good luck.