.3125" would look more prototypical but the .25" will work . what is your bore ? .375" may be to big . In theory , your only picking up the weight of the blade so your not going to need much volume .
here's a lil calculator I pulled off the net . type in your bore , PSI , and rod dia and that will give you what your cylinder can do for given amount of pressure .
http://www.baumhydraulics.com/calculators/cyl_calc.htm