[Cayoterun]

What ever you use, if too much gunk turns loose too fast, there's always the danger of plugging the oil pump screen. Change oil often after flushing.
I've had good results with using a light weight, cheap, high detergent oil, and changing oil and filter when color on dipstick gets dark.

Good luck and enjoy the ol' girl.
It's good to see people bring them back out of a long hibernation like you have.