I would use the ram below to be on the safe side!
http://www.ebay.com.au/itm/1-37-64-B...wAAOSw5dNWq0VA
The ram below is the neat twin cylinder unit but the bore is pretty small. To work out force just multiply airline pressure by the total piston area in square inches - this will give you the holding force. It will be a bit low but you can compensate a bit by running a strip of emery along the back face. You would need three rams per side. You cant go wrong with this stuff though as there are multiple uses and you do need a variety of sizes and these prices are crazy cheap but still work really well.
http://www.ebay.com.au/itm/Alloy-Dou...8AAOSwpzdWq1zr