i have rarely had a patient with a CVA who i felt needed strengthening of the gastrocs... most of mine have had weakness with the dorsiflexors-- therefore ANY strengthening of the gastrocs would simply shift the balance of power even FURTHER from normal.....
why would you EVER think that you needed to strengthen the gastrocs...? i know that with neuro patients there is no such thing as a rule that can't be broken, but seriously, i'd only ever strengthen the gastrocs if the patient was VERY high-level and had acheived full dorsiflexion with 5/5 MMT and full EVERSION with 5/5 MMT.....
and at that point why would you need to ask? for a patient like that you should try........ oh, i don't know---- heel raises???
good luck...