Engine oil problems

I would top off with summer weight oil and cycle it around with the kick start several times. Pull the plug out to make it easier.
You might also put a speedhandle and socket on the flywheel (like you would if you were cycling engine to set valves). Maybe use and air wrench to cycle it around.
Cycle and drain, cycle and drain. Just to make sure you’re getting fresh oil up in the head.
I have heard people using seafoam to clean out the crankcase. But I haven’t needed to. Lotsa sludge can build up in the bottom and that’s where the oil pickups are

if you want to try it, I found instructions for Seafoam use in crankcase on their website.
you might also be able to churn out some of that gunk by opening up the oil filter cover.
Just don’t rotate the engine to fast—careful with all those bearings

INSTRUCTIONS

• First determine the engine’s crankcase oil capacity. Most autos and light trucks have 5 or 6 quart systems. Check in your vehicle’s owner’s manual for the size of your crankcase. One 16 ounce can of Sea Foam Motor Treatment treats up to 16 quarts of oil.
• Add one ounce of Sea Foam Motor Treatment for every quart of oil in the crankcase. When ready, remove oil filler cap and pour the recommended amount of Sea Foam directly into the engine crankcase. Do not exceed one treatment per oil change interval.