What are some similarities between Silky Bob and Jimmy Wells in "After Twenty Years"?

Silky Bob and Jimmy Wells are both good friends and keep promises.

It is pretty remarkable that both Silky Bob and Jimmy Wells showed up to keep a date made twenty years before.  They either are good friends, or men of their word.  We know that Jimmy Wells is a man of honor.  Being a cop is important to him.

The policeman on the beat moved up the avenue impressively. The impressiveness was habitual and not for show, for spectators were few. The time was barely 10 o'clock at night, but chilly gusts of wind with a taste of rain in them had well nigh depeopled the streets.

In other words, Jimmy Wells is a cop through and through.  Bob says he is trustworthy.  This is why he turns in his friend, even though the friend in him does not want to.  He is also an honorable man, which is why he gets another cop to do it.  He can’t bring himself to do it.

Jimmy is also sure that he can depend on Bob.

"Bless my heart!" exclaimed the new arrival, grasping both the other's hands with his own. "It's Bob, sure as fate. I was certain I'd find you here if you were still in existence. Well, well, well! --twenty years is a long time.

Of course, Bob has turned out to be a criminal.  Nobody’s perfect.  Still, he kept his word.  He came when he agreed to.  Bob may be Silky Bob from Chicago, Wanted Man, but he is also the same reliable Bob who made a promise twenty years ago and kept it.  This is another reason Jimmy does not want to turn him in.  He is aware that Bob showed up only because he was keeping a promise.  The Bob who showed up was the old Bob, the Bob from twenty years ago.