Your gut has been right so far. Stick with it. Personally, there's no way I'd just fix one valve & call it good. Either have a complete new set of valves, locks & retainers installed or run your iron heads. Losing the tip of the valve is not common. Either really poor hardening, chinese valves, wrong locks, etc. I run isky iron adjustable rockers on my small block street car. Been in service since 1988. Never an issue. Very similar to the 273 rockers.

Also, while your swapping the heads, you'll be able to inspect all cam lobes & check each lifter. Make sure to lube all the lobes again (don't mix up the lifters).