Honestly all ANSI Model M's that are the size like your backspace do not have any springs around the barrels. Are these springs IBM factory added as a part of the keyboard, or maeby they had as an sidegrade for people that wanted to have more stiff feel to some keys? I have never seen Model M with springs around the barrels.
Remove the springs and see how the clicking feels then, this might be added as an extra by whoever was using that board due to his choice was to have stiffer backspace key?

BTW awesome looking board, open it up and wash it therally, use dental tabs with water for the keys and stems, the casing you can wash with dishwasing detergen and scrub pad, while the plastic plate and the barrel surrounding clean it with cotton swabs and dip them swabs in warmish water with dishwashing detergent.
AT cable looks awesome!!!!!!!!!!