You said that chunks of old oil had already fallen into the engine.
When you take the rocker arms off, more will fall in.
It's probably a good idea to pull the pushrods out as well, remove the oil pan, and flush it from the top. All that crud that fell down into there could easily block a gallery and kill a bearing for you. (I should know, it happened to me with an engine similarly sludged)
Once it's back together, you'll still have whatever was used to flush it inside, so perhaps a 500 mile OCI the first time is in order. After that, frequent oil changes are the way to go as previously mentioned. Any brand name 5w30 dino is what I would use, the least expensive that can be found since you will be going a max of 2000 miles before another change.
IMHO each oil change, be sure to take it on some long runs so it can get good and hot; short tripping this engine isn't going to help things.
In the engine I killed, it ran fine for about 1/2 hour before a bearing went; so the first few drives after surgery, recommending you stay close to home.
Good luck saving this one! Please post back to continue the story.