Hi Sarah,
I'm a physiotherapist working in Ireland. I would suggest you find a physiotherapist who specialises in dry needling and orthotic prescription. Your calf sounds like it is totally overloaded with trigger points and it cant release or stretch out properly. Strengthening will only increase them and lead to further problems. Dry needling is so effective for this. You may need a few sessions though because you have had it for so long and because you want get the muscle right for hight impact long distance running. The craps can also be a sign of myofascial dysfunction. Sometimes i have patients attending the clinic just to have dry needling to relieve calf craps - Works really well! The other thing is you would need to have your feet either assessed by a chartered physiotherapist who is trained in orthotic prescription or a podiatrists. The reason for this is that it sounds to me that you may have a over pronated foot type and as a result of this you are over loading the muscles along the front of the shin ( tibialis anterior muscle) and the calf. Let me know how you get on? Good luck..Lynsey