I believe, but cannot say 100%, that the installation will still happen successfully. You may not encounter any problems for some time, but you could run out of LTS space much quicker. There will also be callouts in the UI that show something to the effect of "this node does not meet minimum requirements for a SMALL tier".
Are you saying that the node has only been giving 600 MB for long term storage? If that is the case I would not recommend installing. That will be used up very quickly and data will be lost.