If you don't have the proper freewheel remover tool or a vice, you can often get the body off with a large pair of channel-lock pliers. The body will likely be damaged though. I'd just get a new freewheel and a new chain once this body is off.

If you have the 4 prong tool you can still use it to take off that body. A bike shop might remove it for you for a couple of $ if you can't get it off yourself.

Cheers