I know the next time I fit a new frizzen to an existing lock, I'm likely to try superglue to hold it in place for drilling. I still won't like doing it! Anyway I did one and got it to fit well, then of course it warped a little when I hardened and tempered it... So I had to fit it AGAIN.
Good luck with yours, and have patience. If you get frustrated, walk away for a bit.
Gerald