The B4 wishbones are 5mm longer and the car will be wider. To make the car work with B4 wishbones you will need to flip them and use Losi hubs, it isn't worth it IMHO.
I have spare wishbones, you can lend one and replace it so you'll never be stuck.
A little birdy told me that a certain great shop who attends the nationals will be stocking X-factory parts very soon...
.... DC Racing...