Short answer: Who cares?
Really. This is poster material for “much ado about nothing.”
I got a recent email about this issue. The controversy is whether the Greek word translated “cross” (stauros) refers to a pole or the object t object that church history has handed down to as as the visual emblem of the crucifixion. The debate combatants don’t deny the crucifixion’s historicity, mind you — it’s about whether church tradition got the shape wrong.
Oh, I’m back. Pardon.
I repeat. Who cares? Church tradition has gotten a lot of things wrong. The biblical account has Jesus crucified for the sins of the world on a stauros. If I time traveled and saw it was a pole, that wouldn’t change the event or the biblical record (or its theology).
I think Bill Craig has a nice reply to this one — he got the same question back in 2010.