Grammar

This is something I probably should know already: if one is referring to two people, one living and one dead, in the same sentence, which tense should be used?
For example: “One of many things Woody Allen and Pope Pius X have in common is that neither goes to Temple very often.”

                 or:

“One of many things Woody Allen and Pope Pius X had in common is that neither goes to Temple very often.”

I myself would go with “had in common,” but I’m not entirely sure. The last half of the sentence (“goes to Temple”) sounds entirely wrong to me.

I’ll go sit over here until someone smart comes along and actually helps.

Ideally, you should phrase your statement such that there’s no clash. e.g.

“One of the characteristics that Woody Allen and the late Pope Pius X have in common is a tendancy to skip out on Temple”

If you’re unable to do so, then go with past tense. However, in your example you use the past tense for “had” but then with “goes to temple” you’re throwing in the present which is a no no. More appropriate would be
“One of many things Woody Allen and the late Pope Pius X had in common is that neither went to Temple very often.”

Overall though, this is an odd example, because I’m not sure if the joke is that the Pope doesn’t currently attend Temple because he’s dead, or that he didn’t attend Temple during his life because he’s not Jewish. Your intent will determine how to best phrase it.

I concur with belladonna. Rewrite to avoid the problem.

One of many things that Woody Allen and Pope Pius X have in common is that neither has gone to temple very often.

I would favour the present tense since the Allen is still alive and so he has in common now. To use past tense would mean he no longer has in common, thus either he is dead or now attends temple regularly.

I’d go with the present, too. That’s because they have it in common now. Using the past implies they once had the trait in common, but not any more.

In other words, it’s not an issue that one is dead and the other is not. The issue is that the both share (and still share) a trait. A live person can share a trait with dead one.