You said it, I didn't !
Don't over think the application.
A grade 5 stud might be questionable, but a grade 8 should be adequate.. keep in mind, metallurgy then, wasn't what it is today..
And if you're planning on reconstructing as per the original fabrication, i.e. welding it in.... then you must be aware that not all steels will weld agreeably.
High carbon or alloy steels have been known to create headaches when welded .
If it was me, I'd just thread it in and use Loctite threadlocker and be done with it.
Then slop enough paint on the backside and nobody will be the wiser !