Hmmmmm, IB5 hasnt been used since the MTX75 box came out which is to be found in the very late Escorts, All Focus's and all Mondeos.

The BC box is basically the same as the IB5 but without a gate in the box and a smaller welded clutch arm.

Also the later typer IB5 have a larger main shaft bearing.

Some of the early BC's also had a four bolt bracket for mounting whereby the later ones use a full crossmember.

Trust me, I used to rebuild them for a living.LOL