They can be fun to get mounted, especially with a lot of tension on the deck drive belt. So, loosen that up some first, and get the rear mounts in. Adjust the draft arms (front draft plate) so the front of the deck is about 1/4 inch lower than the rear. The right side deck hanger (for the lift mechanism) is adjustable, to level the deck side to side.
Don't forget to retension the drive belt.
Don't forget to retension the drive belt.