Yes under SC category you stand a great chance to get a seat in GMC Mumbai. You can try in Rajiv Gandhi GMC, Kalwa as it had cutoff around 464 for sc category last year and with your SMR, your marks might be surely above 500. So you stand a good chance in Topiwala GMC, Bombay Central and Cooper GMC, Parle as they also had sc cutoff around 470s itself. 

So yes you do have a high chance of getting in this GMCs of Mumbai. 

Best wishes. Thank you.