Be VERY careful adding any size to your upper body and losing any flexibility in your chest, shoulders, back, or arms
When I was 16, I was clocked at a show case throwing 87mph, with my average fastball being in the 82-84 range. I was 6'2'' 170lbs, had strong legs and a wiry flexible upper body. I caught the bodybuilding bug when I was 17, packed on about 15 pounds to my upper body, gained a ton of strength, looked great, lost flexibility, and ultimately injured my shoulder. Reoccurring rotator cuff tendinitis and constantly getting bigger, now I play first base on a Division III club baseball team, hit 4th in the line up, and am known as "steroid freak" on my team lol.
I would take some time to think about running ANY gear with your goals in mind. A low dose of Test for muscle recovery would be the only thing I would recommend (250mg/wk or so) and really monitoring the flexibility in your upper body would be imperative for you.
Before Pedro Martinez got hurt, he threw 96mph and was no where near your size. His perfect mechanics and the incredible whip in his body are what got him to what he was.
I hope this is helpful and be careful.