Since the tube ends are identical, it only took a heat gun to bend the old tube so it would fit into the new MC.
Later, I discovered that the new MC doesn't push enough fluid (smaller bore) to operate the old slave, but a crossover MC was available.
...and even later: I learned it's supplied with a crappy bushing.
After THAT, I learned that even a good bushing doesn't stand up to a misaligned cross-shaft.