Are you sure of your sizes? Gars are very rigid and don't bend. With the numbers you provided, I'd expect that some portion of the gar would be sticking out of the TSN's mouth and the gar would be gradually swallowed and digested.
Should not be too much of a shock. Gars are slender. TSN mouths extend huge. If any fish can even remotely fit into a highly predatory catfish mouth girth-wise (not length-wise), it is at risk.