I?m building one myself at the moment. The best body for Stallone with seamless arms is the Hot Toys Rocky body but as that is extremely rare, the next best is the one I?m using which is the Coomodel copy of that body. Even that?s not easy to find but should be around with a bit or searching.
T-shirt wise, the Barney Ross one is definitely the best however I managed to rip mine taking it on and off too much so I ended up with an eBay third party one which is very close to the Barney Ross one.
For trousers I just used a pair of combat ones I got off eBay ages ago.
Boots I?m using Hot Toys Captain America ones as they are pretty close to what he actually wore.
Finally, I had the belt and gun holster made by Gustavo Bautista Ponce who you can find on eBay under his business page ?Old Traveler Workshop?
Good luck and feel free to ask any other questions as I?ve been through a lot of pain building mine.