Well it's true what they say about deadlifts, they add mass on to your forearms like no other excercise. Problem is I use a mixed overhand grip and always use my left hand overhang and right supinated as this seems natural and most comfortable. I think this may be what has lead to my left forearm being half an inch bigger ( no wanking jokes please haha ,I'm right handed). Is this a fair diagnosis of the issue or could it be other things causing it? I dont do any real forearm work besides static holds and shrugs with bb. Same problem with my right calf ,it's an inch smaller than my left calf. I want to get on this before I cause major imbalances in strength , don't want to injure myself. Advice? Should I switch up the grips and do some single arm/ calf work?

It's normal to have a muscle on one side of the body that's larger than its mate on the other side. It's only a problem if a strength imbalance does exist. You can diagnosis this through unilateral exercises. If you find that you do have a strength imbalance then switch to primarily unilateral exercises and always work your weak side first and never do more with the strong side than you can with the weak -- this includes weight as well as set / reps. If you're aggressive with your progress on your weak side, the two will quickly catch up.

In the case of your forearms, unless you find that you can curl or extend more on unilateral wrist exercises, just stick to a left under, right over grip until it equals out. Afterwards, be sure to swap your mixed grip between work sets if you choose to keep using it. Alternatively, and I think better if you have sufficient strength is to immediately switch to a double overhand grip and hook it (http://jva.ontariostrongman.ca/HOOK.htm) if necessary.

Ok thanks a lot , I've wanted to try a hook grip so I will after I equalize the arms by switching grips. I think there is a minor strength difference as I've noticed it on chest pressing excercises to some extent. Hopefully some db calf raises or single leg raises can equalize that out too , my left leg is a bit longer I think and that may be whats causing the imbalance.

Yeah I think this sort of thing is common is most people. I am left handed but all my right side muscles are bigger calf, bicep, tricep, forearm, and pec. They just look more defined than my left side, it sucks but I think it will get better over time. I don't have any strenth issues with it though. My right side is always more sore than the left after I lift too.