Lash is the same as "gap" its the measurement you do with the feeler gauge between the top of the valve stem and the rocker arm. Thanks for the vote Bob but not knowing how long I'm going to be anywhere just now makes sending it to me rather impractical. Heaven knows when I'll have a proper shop again.
TFFs suggestion of metholated spirits is s good one, but like he said lubricate with after run oil afterward unless you get it running somewhat quickly after flushing. As for after run oil there's various ones you can choose, I like Marvel Mystery oil, especially their air tool oil, it has extra rust inhibitors, get it on Amazon.