Bolts missing (?) on Spring Bar bracket (hitch)

No bolts are necessary in ordinary installations. The only purpose of that large bolt on the back side is to keep the brackets from sliding back and forth during turns. If you have enough chain links (at least 5) between the snap up bracket hook and the bars (under tension) then you should be ok.

Sometimes bolting the brackets on through those holes is necessary on very heavy tongue weight trailers, that require strong WD bars, to keep the brackets from bending.
Barney