As far as I recall, the pin in the follower is what's holding...
- compress the spring and hold it in place
- use proper punch to drive out the pin
Yours doesn't look too bad
Where did you get the new one?
- That's quite the change on the cup design. I'd assume it works just has well as the old (smaller, cup). Maybe one could reshape their old buffer?
Let us know how it works (or snap a picture after a few hundred rounds)
- Did you put a fresh spring, while having apart?