My basic theory is to keep clean oil in it. That is change it (and the filter) when it gets dirty, which by your description may be every 3000 feet. The reasoning is you don't want to clean it too fast and loosen a chunk only to have it get stuck someplace worse (aka stroke.) Use diesel oil, its basically gas oil with more deteregent. An additional trick: after the engine has drained, pore a little clean oil in untill clean oil comes out, that will give you a little more cleaning.
You basically have a ruined engine so you won't lose much by experimenting.