HRAP EX Back and Start button size?


Discovered SRK while searching for infos about sticks since I’m gearing up for SFIV. I ordered an HRAP Ex for the 360 and I was planning to replace all the buttons with Sanwa OBSF-30 but just one question, what size are the back and start buttons? I’m not sure if they are the same size as the other buttons. And also, replacing them should be almost as easy as plug and play right?