If the 616 has a freeze plug bolt like the 617 Turbo, I sprung for a 3/4" drove, 19mm allen socket. Made the job a snap, ran about $40 I think. Made the job easy once I pulled the turbocharger and starter came out too I believe.
Sure, I live in Texas but it does drop into the upper teens at times in the winter. I plug it in usually under about 45°F as it is less wear on the motor and I like having heat when it first starts.
Maybe we can work a deal for you to borrow the socket. Drop me a PM