I think my 352 has had a No7 in it at some time as you can see rust pitting in two strips across the steel truck bed about 4 inches wide, one at the rear and one at the front.
There are 8 holes in pairs so two at front left just either side of the chassis rail then the same for front right and rear left and rear right. These were for the fixing of the No7 set and had long studs which passed through the base plates of the No7 then the bed floor ran down past either side of the chassis rails and then had a plate cross ways under the chassis rails to hold it all tight, similar to the bed mounts but longer studs to pass through the bed floor and No7 set base plates.