Don't use concrete grout. It shirks big time and does not adhere to the cylinder walls.
Use Hard Block and it won't pull away. I think it would be better to have a set of deck plates bolted to the block when it is filled and left there for the maching operations, but that is usually not practicle and most deck plates are solid. So you level the block after cleaning it with a muratic acid-water solution and letting all that dry, you level the block both ays and pour one side slowly while getting a helper to beat it with a rubber hammer. Let it sit a full day and repaet the process on the other bank.
There are some other epoxies to use but never use a concrete grout.
Ed