I'd be happy with a "half mod of drivers and crossovers less the triple wall, which is really why the speakers have to be sent back. Some WGH sourced braces supplied perhaps? Sounds interesting!
I have never seen or heard a VR-4 JR, but if they are constructed similar to the VR-2's then just replacing the speakers without adding any additional bracing or some sort of triple wall will only get you half way to nirvana.
I have listened to my VR-2's in four different configurations:
1) Stock with lead shot - pleasant with diffuse imaging and ripe bass
2) Cabinet sides with braces - improved imaging, slightly better bass
3) Additional braces added that connect opposite cabinet sides - bass now has punch and definition
4) Richlite dampening glued between braces - speakers disappear, solid center imaging, OMG bass
There is a strong possibility that the new drivers will have more forceful bass which will excite and vibrate the stock (un-reinforced) cabinets even more making the resulting sound more boomy with diffuse imaging because at every frequency the cabinets vibrate the center image will pull toward that speaker.
Wayne