If you are referring to the area under the side cover I would pull the lifters keeping them in order in storage. Then plug ALL
the lifter bores with shop rags and hand scrape the sludge off as best you can. Vacuum out the sludge than spray the area with
aerosol brake cleaner until it's clean enough for you. Pull the rags, spray inside the lifter bores with the brake cleaner, wipe the bores clean than clean and lubricate the lifters as you reinstall them in order. Your are correct that any liquid runoff will likely run out the bottom of the block, but not all solids.The least thing you want is for any solids to plug oil galleys restricting or shutting off oil flow.
A compressed air gun is useful in blowing out loose junk too.
