Full body = 2k bolt
P-block = "Evo" size
The p-block design uses a shorter bolt because the block actually extends into the body of the cocker.
you said you have a full body cocker so you need the 2k bolt, any 2k bolt will work for you.
if it says P-block design or short bolt then it is for the P-block.
The P-block is a better design because it allows the bolt air inlet hole to exactly line up with the hole in the body for maximum efficiency.
P.S. Polish guy, you know cockers, c'mon
just because it is an Osiris doesn't mean it is still not 90% autococker