I don't know much about Zahn or Lightfoot, but I would think Harnack's and Funk's methodologies would force them to the shorter version no matter what the case. One of the top rules of the Bib-Crits is the shorter the text, the more likely its original. Not the most objective standard, but at least they seem to be consistent.
Harnack is famous, among other things, rejecting major doctrines of Christianity such as the Virgin birth, the deity and pre-existence of Jesus, the Resurrection of the body, the possibility of miracles, the existence of demons, exorcism and Jesus as the promised Messiah. But, other than that, he's a good Proddie.
Funk is the founder of the Jesus Seminar. Next.
Lightfoot has good credentials (as far as I can see) and is quite the language expert.
Zahn - not Paula, I suppose. Not finding much in the way of Zahnian Biblical scholarship.
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Try Theodor Zahn - he's a big name in Evangelical biblical scholarship. Surprised you never heard of him.
Here is the Lightfoot translation. Although he does acknowledge the Ignatius letter as authentic, he translates universal in lieu of Catholic church.
8:6 Wheresoever the bishop shall appear, there let the people be;
8:7 even as where Jesus may be, there is the universal Church.
Still looking for the Paula Zahn translation.-:)