Lots of arms, possibly the hubs, c-block, steering knuckle, shock towers. hinge pins in case they fall out and you can't find them.
everything else should hold out just fine.
Did you contact HPI about getting the revised set of arms? They were giving away 4 pairs of front and rears long while ago along with the revised diffs. Don't know if that offer is still good... you may want to contact there customer service and find out.
good luck with your Pro3.