Another option to secure the end of the reefing
line to the boom is to tie around the boom with a bowline.
This is how I do it as I believe it is stronger that a pad eye screwed or riveted to the boom. You do need either a loose footed main or small slots that are sometimes put in mains with an attached foot so you can get the
line around the boom.
I would go with 3/8"
line, something like Stayset should work.
Gary