Your description suggests that the carriage may be locked.  Can you move the lever in the upper left part of the keyboard? I am wondering if that isn't the carriage lock release.

The lever located top left of the keyboard is the ribbon reverse and has nothing to do with the reported issue. 

Mintdee, the part that is hitting the carriage rail is the carriage lock. In your photo it is in the unlocked position, but it has been bent downward which is why your carriage is being stopped. That part should be parallel to the platen - not pointing downward - so it will clear the carriage rail.

My guess is that the lock was engaged and someone had tried to force the carriage to the left and as a result bent it. To fix it, you will need to move the carriage to the right, and use two needle nose pliers to bend it back into the proper position. Use one of the pliers to support the lever and prevent it from moving where it pivots on the carriage and the other plier to gently straighten the bent section (bend the tip of it upward).

The carriage lock is engaged by moving the carriage to the right, pressing down on the carriage release lever that is between the right platen knob and the carriage, and moving the carriage back until the lock lever fits into the slot that you can see in your photo, which is to the right of the where the lever is now.

It's a fairly simple repair that should only take a few seconds, but if none of this makes sense then just let me know and I'll try to post a few photos as visual aids. 

Technically, the lever is actually called the Carriage Centering Lever and doesn't fully immobilize the carriage, but that was the system that Smith-Corona used at the time in conjunction with the machine's travel case.

Here are the photos that should help: