I'm building a new cross bike. My prior one, to be my B bike, is configured as a 1x9. I ran a 42T Shimano ring in the inner position with a outer guard and an ngear inner guide. I'm going to build with a single front ring again. Should I get another Shimano ring, that's meant to go in the inner position, or get something else.

I stumbled across this on cyclocross world:
https://cyclocrossworld.stores.yahoo....ochforsir.html

It's described as not having any offset. Will this give me some better chain line or should I stick to what I already tried?

Single rings are easy. Since there's no shifting, there's no need for things like ramps, pins, cut down teeth or any of that nonsense. Buy any standard ring and it can be mounted in either the inner (middle) or outer position.