I just went out and looked at mine.They have nut and bolt and large diameter washers holding them in place.I could not see the left rear bolt coming through the underside of the floor pan.I'm thinking it's in the belly area of the floor pan.Stick your hand through the access area under the drivers seat and see if you can feel it.If you need the mounts,tony at 4-5-6 Chevy trucks has them.They can be used on 1947-1966,tony measured mine and they are exactly the same.
jump seat mounting kit
