It seems to me that I should clean the rust out of the injector hole.
I would say 5) reassemble as is.
The penetrating oil dissolves most of the problem rust.
Just put it back together.
1) Evapo Rust put in the cylinder ? sounds bad idea.
2) Machine a plug for the bottom of the injector hole ? bad what if it gets stuck
3) Hardest. Remove the head and clean it without the head on the block.?
Yes best is this, only way to guarantee you dont put grit in the cylinders
4) Other. Use a bore cleaning
kit for a shotgun and clean it that way.
loose bits of rust or pieces of brush falling into the chamber, this is something you have to decide if it is worth doing.