I have seen several sources using the vintage ruling pen (aka drafting pen, draftsman's pen, technical pen), here is one example: I am attempting to use one now to do some lug lining but am not near as proficient as the guy in the video. Knocked over my can of one-shot just yesterday, sigh.....
In poking around, I see there might be more modern, refillable, technical pens, something like that might be worth experimenting with. Really seems like you could get thinner lines with these than with a brush:
https://www.jetpens.com/blog/the-bes...ng-pens/pt/436