The finish kit (for my 6A) appeared to have a lot of extra room in the box - if I was doing it again , I would have asked Van's if the firewall forward kit would fit in the same box, and if so, ordered it as well, and saved the cost of another shipment.
In my case, I need shipment to Canada - so, its an expense worth minimizing to the extent possible.
Bill Brooks
RV-6A fuselage in progree, finish kit in hand.