The most common GC-2 Batteries are 220 amp hours give or take 10
Some companies (IE: Deka) make serveral nearly identical batteries classed as GC-2, 210 to 230 amp hours.. Mine are 230 amp hours and near as I can tell are physically identical (Save for weight) to the 220 amp hour Interstates they replaced. (They are heavier)
Trojan also makes a taller one (NOT a GC-2) that often fits in the same box if you have the height.. 250 amp hours.
Does this help?
Oh, Some companies will use different discharge rates to rate their batteries so they get fantastic numbers.. But the true rating is no different. Most all brands are within 10 percent of 220 AH.