First I would get rid of ALL those miscellaneous bolts holding the check chains, top of the lift arm on left and right, use correct hardened pins for these connections. You don't want one of those lift arm pins to break and have the box blade crawl up the tire and on to your back. I would put some weld metal on that ball end to build it up, looks like at one time it was flipped and someone dragged it down the road for a few miles to wear it off like that.
I am not sure that the check chain attachment point by the PTO shaft is suitable for the stresses of a box blade. It looks like all but one bolt is missing and perhaps someone welded it on to the rear housing. It might be ok if a good weld. Adding those stabilizer would remove the stress from this area.
Of course you do need the correct length top link and some standard pins to attach them, not spare bolts etc. Bolts aren't good for those areas that you have them in, they are too soft, bend or break easily. Get rid of those now before they cause something bad to happen to you or your tractor.
As for stabilizers, it looks like you have an alternate site to attach them which is that bracket under the fender, one seems to already have a pin, but the other side is missing a pin. Alternately you can usually pin them to the same pin that the lift arms are attached to, however on the right side, I cant quite tell what is holding that side on, looks like someone welded on a nut or something, so you may not be able to use that point for your stabilizers. The one under the fender would be a better choice but would require a longer stabilizer bar. Stabilizer bars are basically just a flat bar about 2" wide by 3/8" thick with holes on each end and a slight bend to allow for the angle between the ball end and the attachment end. There are some adjustable ones available that have a slip joint in the middle but I think they would be a little weaker and may tend to slip.
