What are these bolts used for? The one that is threaded, hanging down, is where the body shop connected the rolling frame that held the body shell. It this needed for something or maybe it was just installed to hold the shell on the rolling resto frame?
What is the other bolt for, just behind the reaction plate bolt?
The upper bolts (& nut) are present on mine - not sure of the function as it does not attach anything (though it has one end of the ground connection to the bellhousing on the right side). Possibly it just reinforces/strengthens the frame rail at a point where it would be under a lot of stress.
The bottom hole was empty on mine - perhaps for drainage? I used it to secure a wood pad as that is where I sometimes place a jack stand:
I have holes in my stiffeners fore and aft, possibly as Geo suggested for drainage, but If so I don’t see the point of having them on the ends rather than in the middle. I can’t guess why someone threaded a stud into yours. Perhaps someone had some aftermarket exhaust on it at one point and decided to use it as a hanger point?
The ground strap to the engine is mounted to the upper bolt in mine (I suspect it is also to connect the engine frame to the rail), I don’t think the lower bolt is original.