I have a similar set-up on my car, discs on the front and drums on the rear. I used wide five drums from a '67 Bug on my IRS rear. I also used the narrow shoes from an early Bug. As Al mentioned above, you will have to have a spacer under the axle nut. Using the narrow, wide five drums will help give a little more clearance between the tire and fender.
Another comment, you may not need a narrowed front beam for your disc brake conversion. I used the wide five disc brake kit from CB Performance (not dropped). I have an adjustable front beam that allowed me to set the front to the appropriate height. In my opinion a narrowed beam will push the front wheels too far inboard.
James