Why not knock out the spacer ring that's in the bell housing? Unless I'm mistaken, there is a ring in that hole, as shown in the 2nd picture of post #5.
Fork pivot may become an issue. Look at previous picture.
I'd turn the flange OD as stated previously. Don't forget to add some "lead" to the flange to start in the bell bore. May need to take a little off the 4 bolts also.