Yes it’s drop in the co2 are threaded little bit tricky when changing but easy after a while, it can be changed back to spring, I would think you can fit in a predom, it was made by Laurie Amatruda in uk you can look his name on google
I have two lp53 one is in mint condition in blue silk box,and one is a co2 conversion by Laurie Amatruda which shoots smooth and accurate I also have a predom lutznic which is good to shoot