Here is my way of adding speings to the Rat Rig V-Core bed. These attach to the bed frame. The bracket as such is probably universal for all or most 2020 extrusions. You find Fusion 360 links below. Make the pin as long as you need. The springs I have are 9.8mm outside and approx 5.5mm inside diameter.
This is for me only a temporary solution until I have my final aluminium bed. I dislike 4 point mounts and I prefer the bolts going through the springs instead of besides. The mounting will cause some deflection.