One problem with a pack film conversion is that you need to ensure the pack film sits at the same distance from the lens as the roll film originally - otherwise the focus will be off.
This was my reason for going for 120 conversion, as it meant the film didn't change position from the original.
Its fairly simple to move the front standard retaining mechanism back a bit so the lens to film distance remains the same. This is done for 5x4 conversions as well as pack film.
As stated though, it is easier to convert to 120 as the original film plane can be maintained.