I wouldn't rely on Masteron to deal with gyno. Since you didnt have problems with the first cycle using 500mg of test, it would make sense that 300mg of test would pose even less of an issue. So this would lead me to believe that the problem is probably due to tren, which can effect prolactin and proges. I would continue using your adex but I would also add something in to help block the issues related to tren. Caber, taken at .5mg 2x week should do the trick.
All of that being said, test/prop/tren is a great combo for dieting. I'd consdier it the bread and butter cycle of contest prep.