In this picture from autopower the center eyebolt mount, while the bolt is correctly in tension the tab it goes through sure as hell isn't so thats crap the other two methods are acceptable. Wstar: I checked out the ones in your' journal and the braced and guseted the tabs pretty well, your belt adjusters are pretty close tour seats though it would be better if you could move them towards the bar more, and because you are pulling sideways on the Eye bolt make sure there is a large grade 8 hard washer under the tab and that the eye bolt is severly over rated because it is in at a bad angle check this out for proper use of an eye bolt, I used them at work all the time for lifting and this was part of the saftey course
Eye Bolts That is unless those are just regular bolts under the belt holding the belt tabs down, can't see to well in your pick because the belt covers it.
Locking collars like this which are available from mcmaster are also a great idea if doing the belt around a bar method so the shoulder belts cant slide around and slip off.
And here we have an awesome roll bar with F'd up belt mounting
and one done correctly minus the bolted together rear supports