You can de burr them, but the only thing I use to do that is a Cratex grinding stone, and a very fine grit at that. 320 would be as coarse as I'd go.
The other thing I wanted to mention is the retainer SHOULD snap into the spring. You shouldn't need to beat the retainer into the spring with a hammer, but it should require a good snap to get it on the spring.
If not, the spring will move all around on the retainer and it makes little chips come off the retainer. It also allows the top of the spring to have issues with hysterisis (not sure I spelled that correctly) and once that starts, the spring effectively looses its ability to control the valve earlier than it should. Also, the retainer, if it fits correctly, I'll change the resonance frequency of the spring. Just like a loose fitting retainer will do. I've seen some wild stuff go on with springs if they ain't happy.