Any heim joint 4 link setup I've seen uses bars that are too small to mount bags on. So chances are if you do it you are going to need to add some bar gussets.
I am also thinking you are going to want a poly end on at least one of the bar, otherwise the bar (and lower bag mount) will be able to twist and possibly throw your bags out of whack.
i figured that i would have to run bar gussets but the bar doesn't move a whole lot.My guess would be that the bag would keep the bar from moving a bunch so it shouldn't do that much damage to the bag.No worse than if was mounted on the rear housing.I could be wrong.
No, if you have a heim at each end, the bag will want to twist the bar one way. Once it gets into a groove it will always twist it in that direction. You need a bushing at one end if you have bars on bars, period.
if you were to build a bar so that the lower bag mount is actually below the centerline of the bar, you can get away with a bar with heims on both ends. The bag would be pushing the bar centered instead of over.