This how we put our post up, We tend to do a little over-kill on the farm, we don't like re-doing! We dig 4x4x5 deep holes,use 2 loops of form wire,and have fiber added to concrete.We cut a 18"x18" piece of plywood and use that to make a hole pattern from the base of the pole.We us 3 foot x 1" form bolts and space the bottom of the form bolts with 3/4" re-bar.You can use anything,we use 2 2x4 studs laid across the hole to set plywood on,to hold pattern in place while pouring the concrete.Be sure and make sure the bottom of bolt threads are no further than 1/2" from top of finished concrete. We let concrete set about a week before the sign and post go up.It is a good idea to stick a piece of PVC and elbow it up through the form in case you want to wire your light at some time. This should be fine unless you make Mother Nature mad.You said the bolts from the ring to the post are 15/16 bolts,I think the head of the bolts are 15/16 and the bolts are about 1/2".Not trying to correct you, just help,if need more info just send a PM.
Shorty