I wonder how much experience you have with diesel engines.
Because contra pistons are supposed to be "stuck" and only move under running conditions.
Did you try to RUN them?
I'm afraid you ask for suggestions now that the damage has been done.

ruining a cp by attempting to "sand" it is no laughing matter.
I go: AAAAAAAAAAAAAARRRRRRRRGGGGHHHHHH!
Kind Regards, Hans.