There really is no good way of converting from the 20hr rate to the 24 hr rate without knowing a lot more about the batteries. The manufacturer could probably help you out, but suffice it to say it will be a little higher than the 20 hr rate, but probably not much. I really REALLY doubt you're going to pick up 200 amp hours by increasing your time of discharge 20%, but those L16's are monsterous batteries and it is possible. Basically it just means you're going to be lowering your per hour load on them ~17%. In golf cart batteries you will see a big difference between the 75 amp rates and the 25 amp rates in terms of reserve capacity (another way of stating AH capacity), but that's a tremendous difference.
If you wanted to know the true rate after factoring in Peukert's exponent the best method would probably be to call the manufacturer or a distributer of the batteries (I don't have that info on the L16's handy). I think you will find, however, that it is in the neighborhood of 1300-1350 AH, not a drastic increase.
So you're looking at twelve L16's, eh? That's a tremendous amount of weight.
I wish there were a better option I could give you, but other than looking at forklift batteries (which are often L16's anyway) you're kind of stuck. I will say that I can get in a GC2 case size with 245 amp hours made by East Penn for $150 retail or thereabouts. It would mean even more weight and even more floor space occupied by batteries, but at that price you could run 24 and get a capacity of 1470 amp hours. I know our store would give you a discount on 24 batteries. I would hope your local retailer would do the same. Heck, they might just do it on those L16's if you're buying 12 of them.