I never found a drop in upgrade for the stock latch. If they're worn out and need replacing find NOS parts. The current repros are nothing but a headache. If they just need adjustment, visit Alan Horvaths's site:
http://alanhorvath.com/54chevy/doorlatch.php

I installed Bearclaws a year and a half ago and I've never had to think about them again. It is some work, but it's worth it.

http://www.chuckthetruck.com/page23.html