Snap a photo and post it here if you'd like confirmation. Frankly though if GC2's fit in the compartment and can be adequately secured, then they're the best value in lead acid that you're going to find anyway. An easy way to tell 6v from 12v is to count the number of cells, indicated by the cell caps. 6v has three cells per battery, 12v has six. The second way to determine the battery is case size, LxWxH. Both 6v and 12v batteries have standard/common case sizes and the type can readily be determined that way. If the labels are missing sometimes you can figure out the manufacturer by a date stamp or other marking on the case or terminals. Thinking that's of limited value at this point but I've used it to determine the origin of some house branded batteries.
Mark B.
Albuquerque, NM