Is this a limber chest for the prairie carriage? Or is it an ammunition chest for the pack mule arrangement?

I'm looking at the Confederate Ordnance Manual which appears to be a distillation and adaptation of the earlier Federal manual. It says on pg. 91 that both the "prairie" and mountain howitzer carried 8 rounds per chest with the following listing:
Shells------------------1 Left end
Spherical case, fixed---6 Middle
Canister, fixed---------1 Right end
Friction primers-------12 In water proof paper.
Slow match (yard)------1/2
Portfires,--------------1

There would be 3 mules with 2 ammunition chests each for the mountain howitzer set up, I'm not sure about the limber chest for the prairie howitzer. It was a cut down size, but it might have carried two ammunition chests worth of ammo or something like that. (There is a carriage builder that builds these somewhere on the web you might look for that. I think Prairie Grove, Arkansas' visitor center has one on diplay as well so a call there might yield some info.)

Implements and equipment listed for the prairie carriage are (page 93)
Sponges and rammer-------------2 On carriage
Sponge covers------------------2 " "
Handspike----------------------1 " "
Vent cover---------------------1 On the gun
Haversack----------------------1 In ammunition chests
Tube pouch---------------------2 " "
Priming Wire-------------------1 In the tube pouch
Thumb Stalls-------------------2 " "
Gunners gimlet-----------------1 " "
Lanyard for friction primers---2 " "
Fuze cutter--------------------1 " "
Gunner's pincers---------------1 In tool chest A
Tarpaulin (6'x10')-------------1 On the ammunition chest
Water bucket-------------------1 On the limber
Prolonge-----------------------1 On the gun carriage
Tar bucket---------------------1 On the limber

Implements and equipment listed for the mountain carriage are (page 93)
Sponges and rammer-------------1 On carriage
Sponge covers------------------1 On the sponge
Handspike----------------------1 On the carriage
Vent cover---------------------1 On the gun
Haversack----------------------1 On pack with ammo chest
Tube pouch---------------------2 " "
Priming Wire-------------------1 In the tube pouch
Gunners gimlet-----------------1 " "
Lanyard for friction primers---2 " "
Fuze cutter--------------------1 " "
Gunner's pincers---------------1 In tool chest A
Tarpaulin (5'x5')--------------1 On pack with ammo chest