I went through the same thing a few months ago. I wound up asking Channing Chen during a community Zoom call. The K=series was before his time, but he said that if it wasn't on the legacy site, chances were that it was one of the few that they'd never gotten around to writing a manual for.
I would have suggested d/l'ing the K-27 manual, but the suggestion to use the K-36 manual is probably just as valid. As for lighting it off, Cliff Luscher recommended using one of those flexible 'sparky' lighters to get in front of the 'hidden' flue and light that one first; the turbulence from the flame in the other flue can cause difficulties. I've tried this, and using the sparker has ignited both burners every time -- at least so far.
Mine is #475 -- Green boiler, DRGW. Which one is yours?
P.S. Dang it.. I tried to 'reply' from a notification last week, and the site wound up registering me again as 'new.' Apparently, replying from a notification uses this new registration. I'm Gary Woolard; been here for a decade. Does anybody know how to just 'kill' this registration?