Wow! Someone looked it up! Everyone else hazarded a guesstimate.
The three most important words one might share (if one must share) when one doesn't actually know for certain are "I don't know."
Instead of "Just remove them and throw them away."
These are also a most valuable response from the min wage 'associate' in the big Box Store instead of several minutes of speculation wasting my time while they're paid to waste theirs.
I've a B-7800 and I do believe my top link has such screws. I suspect that they are simple caps to the sight holes there to allow one to see if grease has gotten to where it needs be. But I'd have to read my manual before concluding as much.
I would agree with those suggesting that screws long enough to contact the threaded portions of the top link would, if tightened nicely, screw up the threads of that part of the link they were intended to secure.
Removing the link might well facilitate the application of some penetrating lubricant, use of a vise to hold a part of it steady while attempting to 'free it up.' And removing those screws and looking into the voids might offer some insight into the sticky situation.
It might allow one to determine which of the ends were stuck - if not both, of course.
?