Not familiar with this particular model, but usually the transmission is mounted in slotted holes to allow for chain adjustment.
On the other hand, if you are able to put the chain back on as you say, it indicates WAY to much slack. Either the wrong chain (too long) is fitted (in which case remove 1 or more links), or it's worn almost to the point of falling apart. Any mower shop should be able supply a new chain.
phil_saunders@bigfoot.com
Phil Saunders, June 2008