Bolt substitution for rivets

[72tutone]

I known this has posted several times, however I'm having difficulty finding the right size 7/16-14 bolt length. I have read postings where I need to find a bolt with at least 1/4 shank on the bolt. Most of the bolts I'm finding have much more than that. My concern if the shank is too long I wont be able to snug the nylock but all the way down.
I have also read some are tapping the whole and just screwing the bolt into the frame.
Any thoughts would be appreciative.
These are frame reinforcement plates these would be going into.