The book/story starts with the author, perhaps an atheist, appearing on a talk show and upon leaving the show, has some sort of accident, and wakes up in the time of Jesus.
That's as close to Behold the Man as it gets, because he doesn't replace Jesus on the cross, but witnesses the life of Jesus, and as the story closes, he received a pendant from one of the disciples. It's this pendant that in turn saves his life, when a soldier/centurion/plain old spear thrower, hits him in the chest with a spear.
He wakes up in the present, imagining it all to be a dream, but with a sore chest he attributes to the accident he had earlier, goes to rub his chest and finds the pendant with a dent in it where the spear would have hit.
I've been looking for this book, or at least it's title, since the early 90's so it's something written before then, I imagine 70's or 80's.