Does the attachment method need to completely clear the L brackets the square tubing rides/slides within?
Are you even looking for suggestions, or just indicating that you are merely pondering the possibly imponderable?
If it must clear the L bracket, I think I would use a large, thick washer,and cut it out so it resembles a U. then drill 2 holes in the washer that match the square tubing on one side of the 'U', and one hole on the other side of the U for the Actuator.
Are you being a good battery owner and keeping those new 6 volts on a trickle charger, or recharging weekly or every few weeks at least?