I've been rounding square plug and bolt heads using crescent adjustable, open end, box end wrenches and 8 and 12 point sockets for sixty years. Why didn't anybody tell me about this:

Take 2 sockets of the same size and matching a long nut used for connecting ready rod and available at any hardware store. In my example I used two 7/16 sockets with 3/8 drive. Line the sockets nose to nose with the long nut (7/16 OD in my case) in between and use the 3/8 drive end on the square plug or bolt and the other on the ratchet. You could also use a piece of hex stock between the sockets. Live and learn.

The tool is limited to the socket drive sizes, but 1/4, 3/8, and 1/2 take care of a very high percentage of the square headed fastenings we'll encounter with our LBCs. The masking tape holds the sockets together on the nut. Live and learn.
square socket.jpg
Tom