According to the Victor Data Book (Robert Baumbach), the VV-XI's Exhibition sound box was phased out in favor of the #2 sound box in 1919, which would correspond with serial number range 498000-620000 (SEE GRID ON THIS PAGE --
http://www.victor-victrola.com/XI.htm )
I'd say, if your machine was manufactured from about 1918 onward, the #2 sound box would be correct, since Victor dealers often upgraded sound boxes of the yet to be sold floor models, and many remained in stock for several years, depending on the location.
Along this line, since the #2 was sold to customers directly as an upgrade, it would also be considered correct for any type of of (pre-Orthophonic) Victrola.
So, even if this is an earlier model XI, the #2 sound box would not be
incorrect. Since this is a relatively low end model***, I wouldn't make the investment in a replacement Exhibition sound box. The #2, if properly restored, will give you a louder, and fuller tone, anyway.
***This assumes the upright cabinet model. If this is one of the relatively rare, very early table model versions, then I'd try to hunt down an Exhibition sound box, using the #2 as a swap/trade-in or a back-up.